BotanicnlJournal o f f h r Linnenn Sonet?, 80: 9 1- 124. With 1 figures
Fcbi-u;ii.\- 1980
A revised system of classification
of the angiosperms
R. M. T. DAHLGREN
Botanical Museum ofthe C‘niversity of Copenhagen,
Gothersgade 130, D K 1123 Copenhagen, Denmark
A [cr,b/p(I f . r publication Orcernber / 979
A new \vstetii of classification of the angiosperms is presented. Like that of Dahlgren. 1975. i t is
\Iio\vti n; a tw(i-diinensional diagram or frame-work, but differs in numerous major and minor
lenturcs. I n the tiew classification the angiosperms represent a class divisible into two subclasses corI-csponditig to the di- and monocotyledons. The dicotyledons are divided into 24 ruperorders, viz.
tlir Magnoliiflorae, Nynphaeiflorae, Ranunculiflorae, Caryophylliflorae, Polygoniflorae,
Mnlvilloi-ae, Violiflorae, Theiflorae, Prirnuliflorae, Rosiflorae, Podostemoniflorae, FabiHorae,
Proteillorae, Myrtiflorae, Rutiflorae, Santaliflorae, Balanophoriflorae, Araliiflorae, Asteriflorar,
Solmifioi-ae, Corniflorae, LoasiHorae, Gentianiflorae a nd Lamiiflorae, while the monocotyledons
r ~ t - cdivided into reven superorders, the Alismatiflorae, Ariflorae, Triuridiflorae. Liliiflorae,
Zirigil)c~i-illorae,C:oniineliniflorae and Areciflorae. The higher categories a re not defined here, but
\oinc general teatures in the classification are mentioned, a nd the distribution of some attributes is
\Iiown i n the diagram.
KEY WORDS :- angiosperm classification - Liliidae - Magnoliidae - Magnoliopsida.
CONTENTS
1111 t-otitrctioii
. . . . . . .
The classification , .
. . . . . . .
.Ihc family k v c l
. . . . . . .
Sonic fcnturc-\ oft he clasihcation
. . . . .
The diagratn. possibilities and limitations
. .
Distribution ofsoine attributes in thediagram
.
S\-niprtalous flowers
. . . . . . .
Liiitegrnic o v u l r \
. . .
. .
Presence of parietal cells
. . . . . .
Endoapn-in forination
. . . . . . .
S o i n e c-hemical coiripounds
. . . . .
Tlre m o i i ~ ~ c o t ~ l r d o t i s
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Pi-ospectives, I-elation to other current classihcations
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I22
INTRODUCTION
A provisional system of classification of the angiosperms was presented in 1975
(Dahlgren, 1975a). A diagram showing the angiosperm orders as figures
(‘bubbles’) was given in which the relative numbers of species involved were
0024-4074/80/02009 1 + 34/$02.00/0
I
91
0 1980 The Ltnnean Socier\ of London
92
R. M . T. DAHLGREN
indicated by the size of the figures. Their relative positions approximated to the
mutual similarity of attributes reflecting phylogenetical affinity.
This diagram has been used in a number of publications cited below to
illustrate the distribution ofvarious attributes :
apocarpy, syncarpy and monocarpellate condition (Dahlgren, 197 7a),
choripetaly, sympetaly (Dahlgren, 1977a, b),
multistaminate gynoecia with different developmental sequence (Dahlgren,
1977a1,
different types of sieve element plastids (Behnke & Dahlgren, 19761,
monoaperturate pollen grains (Dahlgren, 197 7a, b),
sclereid idioblasts (Rao & Das, 1979),
types of microsporogenesis (Dahlgren, 1977a),
bi- and unitegmicovules (Dahlgren, 197513,1977131
tenui-, pseudocrassi- and crassinucellate ovules (Dahlgren, 1975b),
types of endosperm formation (Dahlgren, 197513)
bi-and trinucleate pollen grains (Dahlgren, 1975b)
iridoid compounds (Jensen, Nielsen & Dahlgren, 19751,
ellagic acid and ellagitannins (Dahlgren, 197 7a, b )
benzylisoquinoline alkaloids (Dahlgren, 197 7a, b)
tropane alkaloids (Romeike, 197 8
pyrrolizidine alkaloids (Culvenor, 1978)
polyacetylenes (Dahlgren, 1977a, b)
various classes offlavonoid compounds (Gornall, Bohm & Dahlgren, 1979).
Other attributes, the distributions of which have been plotted in this diagram,
have not been published, such as the seed coat characters presented by Corner
(1976).
More than a hundred different character states have been plotted in a diagram
showing the monocotyledons and the most closely allied dicotyledons (Dahlgren
& Clifford, in press), some material of which will be shown in this article.
These results have, as expected, shown that my provisional classification and
diagram of 1975 could be improved in various respects.
Numerous studies on limited groups or on various attributes have contributed
to their taxonomic position, such as for the Fouquieriaceae (Dahlgren,Jensen &
Nielsen, 1976) and the Retziaceae (Dahlgren, Goldblatt, Nielsen & Rourke,
1979).
In the construction of the classification given here, an attempt has been made
to take into consideration as much information as possible. The new classification is still provisional, but it is appropriate to present it here in its most updated
form.
The purpose that can be achieved in the long run should be a system of
classification as natural as possible in the sense that it reflects, in the position of
each family, phylogenetic relationships. I f this is possible, there is a greater
chance for predicting the occurrence of an attribute of interest (whether it be the
possession of a chemical compound or an embryological feature) or for predicting that a particular, perhaps concealed, attribute is more likely to be found in
certain families or orders than in others. Thus a useful system of classification
would have a predictive value.
This must not be misinterpreted as meaning that all groups with a singular
particular property, for example the synthesis of a group of chemical
ANGIOSPERM CLASSIFICATION
93
compounds, are necessarily related and thus should be in the same part of the
classificatory table o r diagram, because the same attributes may have evolved independently on separate occasions. Closely allied groups of plants may be very
variable with respect to a great number of characters.
However, there is little doubt that closely related plants-when a sufficient
number of their characters has been examined-will normally prove to agree in
more of these characters than will distantly related plants.
In order that a classification can be useful for the sake of prediction, it must
also be complemented with diagrams showing the approximate distributions of a
considerable number of attributes.
T H E CLASSIFICATION
In this classification the angiosperms comprise a class, Magnoliopsida,
equivalent to the main groups of the gymnosperms (Pinopsida, Ginkgoopsida,
Cycadopsida, Gnetopsida).
Their division into two main groups, the dicotyledons and monocotyledons,
has often been considered as somewhat arbitrary and would probably not stand a
test according to cladistic methods (see Bremer & Wanntorp, 19771, but the
monocotyledons stand out as a possibly monophyletic group by virtue of their
single cotyledon and characteristic triangular protein bodies in the sieve tube
plastids (Behnke, 1969), in addition to a number of less constant differences from
the dicotyledons. The dicotyledons and monocotyledons have here been given
the rank of subclasses comprising the Magnoliideae and Liliidae respectively,
these entities having thus a circumscription different from, and much broader
than, the classifications of‘ Cronquist (1968) and Takhtajan (1969).
The dicotyledons and monocotyledons are further divided into superorders.
In accordance with Thorne (1968, 1976) these bear the termination -JEorae which
takes precedence over the -anae used by Cronquist (1968) Takhtajan (1969) and
Dahlgren (1975a). A disadvantage with this suffix is that it cannot be used for
superorders of lower plants.
This classification has been worked out gradually in discussions with
colleagues in Europe and North America over a period of years. Rather than
aiming to be conservative it is a radical approach, introducing changes where
reasonable evidence is available.
Thefarnib level
With regard to the Liliiflorae a‘splitter’s’approach has been chosen at the family
level, largely in accordance with the work of Huber ( 1969).This may seem infatory
for a traditionalist used to the Liliaceae sensu lato, and an intermediate level for the
family rank in this group may be feasible or even preferable (p. 106). What is
important in this context are the basic concepts of interrelationships between
the families in the orders presented here, uiz. the Liliales, Asparagales,
Dioscoreales, etc. Thus Alliaceae and Hyacinthaceae representing the subfamilies
Allioideae and Scilloideae respectively of the traditional Liliaceae are very far from
Liliaceae sensu stricto (subfam. Liliodeae), and much closer to Amaryllidaceae,
whereas Colchicaceae (Liliaceae subfam. Colchicoideae and relatives) and
Alstroemeriaceae are indeed close to Liliaceae sensu stricto (subfam. Lilioideae).
R . M. T. DAHLGREN
94
The background for these considerations is explained by Huber (1969) and
also by the author (Dahlgren et al., 1976) and will be further elucidated in a
coming textbook on monocotyledons (Dahlgren & Clifford, in press); the basis is
also partly expressed in my previous classification (Dahlgren, 1975a).
A similar approach is preferred here for the derivatives of the traditional Saxitragaceae sensu lato. This was very heterogenous and consisted of distantly
related elements, which mainly fall into two orders, Saxifragales and Cornales,
though some incidently fall outside these orders (e.g., Parnassiaceae,
Ribesiaceae). Only a thorough study of the small groups recognized as separate
families here and placed for the most part in Cornales, can correctly show the
affinities and most appropriate status and circumscription of each.
CLASS
MAGNOLIOPSIDA (=ANGIOSPERMAE)
SUBCLASS MAGNOLIIDAE (=DICOTYLEDONEAE)
MAGNOLIIFLO RAE
ANNONALES : Annonaceae, Myristicaceae, Eupomaticeae, Canellaceae.
ARISTOLOCHIALES:Aristolochiaceae.
RAFFLESIALES: RafHesiaceae (including Cytinaceae and Mitrastemonaceae),
H ydnoraceae.
Winteraceae, Degeneriaceae, Himantandraceae, Magnoliaceae, Lactoridaceae, Chloranthaceae,
I LLICIALES: I lliciaceae, Schisandraceae.
LAURALES: Amborellaceae, Austrobaileyaceae, Trimeniaceae, Monimiaceae
(including Siparunaceae and Atherospermataceae), Gomortegaceae,
Calycanthaceae (including Idiospermaceae), Lauraceae, Hernandiaceae
(including Gyrocarpaceae).
NELUMBONALES : Nelumbonaceae.
MAGNOLIALES:
NYMPHAEIFLORAE
PIPERALES : Saururaceae, Piperaceae (including Peperomiaceae).
NYMPHAEALES: Cabombaceae, Ceratophyllaceae, Nymphaeaceae
(including
Barclayaceae).
RANUNCULIFLORAE
RANUNCULALES: Lardizabalaceae,
Sargentodoxaceae, Menispermaceae, Kingdoniaceae, Circaeasteraceae, Ranunculaceae (including Hydrastidaceae), Berberidaceae (including Glaucidiaceae, Leonticaceae and Podophyllaceae),
Nandinaceae.
PAPAVERALES : Papaveraceae, Fumariaceae (including Hypecoaceae).
CARYOPHYLLIFLO RAE
CARYOPHYLLALES: Phytolaccaceae (including Achatocarpaceae,
Agdestidaceae
and Limeum), Basellaceae, Portulacaceae, Stegnospermataceae, Nyctaginaceae, Aizoaceae (including Mesembryanthemaceae and Tetragoniaceae),
Didiereaceae, Cactaceae, Hectorellaceae, Halophytaceae, Chenopodiaceae
(including Dysphaniaceae), Amaranthaceae, Molluginaceae, Caryophyllaceae
(including Illecebraceae).
POLYGONIFLORAE
POLYGONALES : Polygonaceae.
ANGIOSPERM CLASSIFICATION
9'
MALVIFLORAE (= Dilleniiflorae)
PAEONIALES: Paeoniaceae.
DILLENIALES : Dilleniaceae.
Sterculiaceae, Elaeocarpaceae, Plagiopteraceae, Bixaceae,
Cochlospermaceae, Cistaceae, Sphaerosepalaceae, Sarcolaenaceae, Huaceae,
Tiliaceae, Dipterocarpaceae, Malvaceae, Bombacaceae.
URTICALES: Ulmaceae, Moraceae, Cecropiaceae, Barbeyaceae, Cannabinaceae,
Urticaceae.
RHAMNALES: Rhamnaceae.
ELAEACNALES : Elaeagnaceae.
PLUMBAGINALES (position uncertain) : Limoniaceae, Plumbaginaceae.
THYM ELAEALES: Thymelaeaceae.
EUPHORBIALES: Euphorbiaceae
(including Picrodendraceae, Hymenocardiaceae and Uapacaceae), Simmondsiaceae, Pandaceae, Aextoxicaceae
(position uncertain), Dichapetalaceae, Didymelaceae (position uncertain;
alternativelv in Buxales).
MALVALES:
VIOLIFLORAE
VIOLALES:
Flacourtiaceae (including Lacistemaceae), Passifloraceae, Dipentodontaceae, Peridiscaceae (position uncertain), Scyphostegiaceae, Violaceae,
Turneraceae, Malesherbiaceae, Achariaceae, Datiscaceae, Begoniaceae,
Cucurbitaceae, Caricaceae.
SALICALES: Salicaceae.
TAMARI CALES : Tamaricaceae, Frankeniaceae.
CAPPARALES: Capparaceae (including Cleomaceae, Pentadiplandraceae and
Koeberliniaceae), Brassicaceae, Tovariaceae, Resedaceae, Gyrostemonaceae,
Batidaceae, Moringaceae (position of the three last families somewhat
uncertain but probably justifiable here; L. Bolt Jsrgensen, personal communication).
SALVADORALES (position uncertain) : Salvadoraceae.
THEIFLORAE
THEALES :
S tachyuraceae,
Pentaphylacaceae
(position
uncertain),
Marcgraviaceae, Quiinaceae,
Ancistrocladaceae, Dioncophyllaceae,
Nepenthaceae, Medusagynaceae (position uncertain), Caryocaraceae,
Strasburgeriaceae, Ochnaceae, Oncothecaceae, Scytopetalaceae (position
uncertain), Lecythidaceae (including Asteranthaceae, Foetidiaceae,
Barringtoniaceae and Napoleonaceae), Theaceae (including Tetrameristaceae
and Pellicieraceae), Hypericaceae (= Clusiaceae), Elatinaceae.
DROSERALES: Droseraceae, Lepuropetalaceae, Parnassiaceae.
PRIM ULI FLO RAE
EBENALES: Ebenaceae, Sapotaceae, Styracaceae, Lissocarpaceae.
PRIMULALES: Myrsinaceae, Aegicerataceae, Theophrastaceae,
Primulaceae,
Coridaceae.
ROSIFLO RAE
TROCHODENDRALES:
Trochodendraceae, Tetracentraceae, Eupteleaceae, Cer-
cidiphyllaceae.
Hamamelidaceae (including Rhodoleiaceae and Altingiaceae), Platanaceae, Myrothamnaceae, Geissolomataceae.
HAMAMELIDALES:
R. M . T. DAHLGREN
96
FAGALES : Fagaceae, Corylaceae, Betulaceae.
BALANOPALES : Balanopaceae.
JUGLANDALES: Rhoipteleaceae,Juglandaceae.
MYRICALES : Myricaceae.
CASUARINALES : Casuarinaceae.
BUXALES: Buxaceae, Daphniphyllaceae.
CUNONIALES: Cunoniaceae, Baueraceae, Ribesiaceae,
Brunelliaceae, Davidsoniaceae, Eucryphiaceae, Bruniaceae, Grubbiaceae.
SAXIFRACILES: Crassulaceae. Cephalotaceae, I teaceae, Francoaceae, Saxifiagaceae, Vahliaceae, Greyiaceae.
GUNNERALES: Gunneraceae.
ROSALES: Crossosomataceae (position uncertain), Rosaceae, Neuradaceae,
Malaceae (= Pomaceae),Amygdalaceae, Chrysobalanaceae.
PODOSTEMIFLORAE
PODOSTEMALES: Podostemaceae (includingTristichaceae).
FABIFLORAE
FABALES : Mimosaceae, Caesalpiniaceae, Fabaceae.
PROTEI FLO RAE
PROTEALES : Proteaceae.
MY RTIFLO RAE
MYRTALES:
Myrtaceae (including Heteropyxidaceae), Psiloxylaceae,
0 liniaceae, Melastomataceae (including Memecylaceae), Penaeaceae, Crypteroniaceae, Lythraceae, Sonneratiaceae, Punicaceae, Combretaceae,
Onagraceae, Trapaceae (position uncertain).
HALORAGALES: Haloragaceae.
RHIZOROPHORALES: Rhizophoraceae (excludingAnisophylloideae).
RUTIFLORAE
RUTALES :
Rutaceae (including Rhabdodendraceae and Flindersiaceae),
Cneoraceae, Surianaceae, Simaroubaceae, Burseraceae, Meliaceae (including
Aitoniaceae).
SAPINDALES: Coriariaceae, Anacardiaceae (including Pistaciaceae and
Julianiaceae), Leitneriaceae, Podoaceae, Sapindaceae (including
Stylobasidiaceae), Hippocastanaceae, Aceraceae, Akanaiceae, Bretschneideraceae (position uncertain), Emblingiaceae, Meliosmaceae, Staphyleaceae, Sabiaceae (position uncertain), Connaraceae, Melianthaceae (position
uncertain).
BALSAMINALES : Balsaminaceae.
POLYGALALES: Malpighiaceae, Trigoniaceae, Vochysiaceae, Polygalaceae
(including Xanthophyllaceaeand Diclidantheraceae),Krameriaceae.
GERANIALES: Zygophyllaceae, Nitrariaceae, Peganaceae, Balanitaceae,
Erythroxylaceae, Humiriaceae, Linaceae, Ctenolophaceae, Ixonanthaceae,
Lepidobotryaceae, Oxalidaceae (including Averrhoaceae), Geraniaceae,
Dirachmaceae, Ledocarpaceae,Vivianiaceae, Biebersteiniaceae.
TRO PAEOLALES (position uncertain) : Tropaeolaceae, Limnanthaceae.
SANTALIFLORAE
CELASTRALES :
Celastraceae (including Hippoaateaceae, Tripterygiaceae,
Siphonodontaceae and Goupiaceae), Stackhousiaceae, Lophopyxidaceae,
ANGIOSPERM CLASSIFICATION
97
Cardiopteridaceae (position uncertain), Corynocarpaceae (position
uncertain).
VITIDALES: Vitidaceae (including Leeaceae).
SANTALALES :
Olacaceae
(including
Octoknemataceae),
Opiliaceae,
Loranthaceae, Misodendraceae, Eremolepidaceae, Santalaceae, Viscaceae.
BALANOPH ORIFLO RAE
BALANOPHORALES (position uncertain) : Cynomoriaceae, Balanophoraceae.
ARALIIFLORAE
PITTOSPORALES:
Pittosporaceae, Tremandraceae (position uncertain), Bybli-
daceae.
ARALIALES :
Helwingiaceae, Araliaceae, Apiaceae.
ASTERIFLORAE
CAMPANULALES:
Pentaphragmataceae, Campanulaceae (including Sphenocleaceae), Lobeliaceae.
ASTERALES : Asteraceae.
SOLANIFLORAE
SOLANALES:
Solanaceae (including Nolanaceae, Duckeodendraceae),
Sclerophylacaceae, Goetzeaceae (position uncertain), Convolvulaceae
(including Humbertiaceae), Cuscutaceae, Cobaeaceae, Polemoniaceae.
BORACINALES: Hydrophyllaceae, Ehretiaceae, Boraginaceae, Wellstediaceae,
Lennoaceae (position uncertain), Hoplestigmataceae (position uncertain).
CORNIFLORAE
FOUQUIERIALES: Fouquieriaceae.
ERICALES: Actinidiaceae (including
Saurauiaceae), Clethraceae, Cyrillaceae,
Ericaceae, Empetraceae, Monotropaceae, Pyrolaceae, Epacridaceae,
Roridulaceae, Diapensiaceae.
EUCOMMIALES : Eucommiaceae.
SARRACENIALES: Sarraceniaceae.
CORNALES : Garryaceae, Alangiaceae, Nyssaceae, Cornaceae, Aucubaceae,
Corokiaceae, Davidiaceae, Torricelliaceae, Phellinaceae, Aquifoliaceae,
Paracryphiaceae, Sphenostemonaceae, Symplocaceae, Anisophyllaceae
(position uncertain), Icacinaceae, Escalloniaceae, Montiniaceae,
Medusandraceae (position uncertain), Columelliaceae, Stylidiaceae (including
Donatiaceae), Alseuosmiaceae, Hydrangeaceae, Dialypetalanthaceae,
Sambucaceae, Adoxaceae, Dulongiaceae, Tribelaceae, Eremosynaceae,
Pterostemonaceae, Tetracarpaeaceae (position and status of the last 5 families
uncertain).
LOASI FLO RAE
LOASALES: Loasaceae.
GENTIANIFLO RAE
GOODENIALES: Goodeniaceae (including Brunoniaceae).
OLEALES: Oleaceae.
GENTIANALES: Loganiaceae (including Antoniaceae, Spigeliaceae,
Strychnaceae, Potaliaceae), Rubiaceae (including Theligonaceae), Menyanthaceae, Gentianaceae, Apocynaceae, Asclepiadaceae.
R. M. T. DAHLGREN
98
LAM I IFLO RAE
SCROPHULARIALES:
Bignoniaceae, Myoporaceae, Gesneriaceae, Buddlejaceae,
Scrophulariaceae (including Nelsoniaceae and Orobanchaceae),
Globulariaceae, Selaginaceae, Stilbaceae, Retziaceae, Plantaginaceae,
Lentibulariaceae, Pedaliaceae, Trapellaceae, Martyniaceae, Acanthaceae,
Thunbergiaceae, Mendonciaceae, Henriqueziaceae (position uncertain).
HIPPURIDALES: Hippuridaceae.
HYDROSTACHYALES (position uncertain, possibly allied to Cunoniales or
Gunnerales in the Rosiflorae): Hydrostachyaceae.
LAMIALES: Verbenaceae (including Phrymaceae, but excluding Stilbaceae),
Callitrichaceae, Lamiaceae.
SUBCLASS
LILIIDAE (=MONOCOTYLEDONEAEI
ALI SMATIFLORAE
HYDROCHARITALES:
Butomaceae, Aponogetonaceae, Hydrocharitaceae (incl.
Thalassiaceae and Halophilaceae).
ALISMATALES : Alismataceae (including Limnocharitaceae).
ZOSTERALES: Scheuchzeriaceae, Juncaginaceae
(including Lilaeaceae),
Najadaceae, Potamogetonaceae (including Ruppiaceae), Zosteraceae,
Posidoniaceae, Cymodoceaceae, Zannichelliaceae.
TRIURIDIFLORAE
TRIURIDALES: Triuridaceae.
ARIFLORAE
ARALES: Araceae, Lemnaceae.
LILIIFLORAE
DIOSCOREALES:
Dioscoreaceae (including S tenomeridaceae), Trichopodaceae,
Taccaceae, S temonaceae (including Croomiaceae),Trilliaceae.
ASPARAGALES: Philesiaceae, Luzuriagaceae, Geitonoplesiaceae, Smilacaceae
(including Ripogonaceae), Petermanniaceae, Convallariaceae, Asparagaceae,
Ruscaceae, Herreriaceae, Dracaenaceae, Nolinaceae, Doryanthaceae,
Dasypogonaceae, Xanthorrhoeaceae, Agadaceae, Hypoxidaceae,
Tecophilaeaceae, Cyanastraceae, Phormiaceae, Dianellaceae, Eriospermaceae,
Asteliaceae, Hanguanaceae (position uncertain), Aphyllanthaceae,
Anthericaceae, Asphodelaceae (including Aloeaceae), Hemerocallidaceae,
Funkiaceae, Hyacinthaceae, Alliaceae (including Agapanthaceae and
Gilliesiaceae),Amaryllidaceae.
HYDATELLALES (position uncertain) : Hydatellaceae.
LILIALES: Colchicaceae, Iridaceae, Geosiridaceae, Calochortaceae, Tricyrtidaceae, Alstroemeriaceae, Liliaceae, Melanthiaceae.
BURMANNIALES: Burmanniaceae, Thismiaceae, Corsiaceae.
ORCHIDALES: Apostasiaceae, Cypripediaceae, Orchidaceae.
VELLOZIALES : Velloziaceae.
BROMELIALES: Bromeliaceae.
HAEMODORALES: Haemodoraceae (including Conostylidaceae).
PONTEDERIALES: Pontederiaceae.
PHILYDRALES: Philydraceae.
TYPHALES: Sparganiaceae, Typhaceae.
ANGIOSPERM CLASSIFICATION
Z I N G I B E RI FLO RAE
ZINGIBERALES:
LOwiaCeae, Musaceae,
Heliconiaceae,
Zingiberaceae, Costaceae, Cannaceae, Marantaceae.
99
Strelitziaceae,
COMMELINIFLORAE
COMMELINALES : Mayacaceae, Commelinaceae (including Cartonemataceae).
ERIOCAULALES: Rapateaceae, Xyridaceae, Eriocaulaceae.
JUNCALES: Thurniaceae, Juncaceae.
CYPERALES : Cyperaceae.
POALES: Restionaceae (including Anarthriaceae and Ecdeiocoleaceae),
Centrolepidaceae, Flagellariaceae, Joinvilleaceae, Poaceae.
ARECIFLORAE
ARECALES: Arecaceae.
CYCLANTHALES: Cyclanthaceae.
PANDANALES : Pandanaceae.
SOME FEATURES OF T H E CLASSIFICATION
The Magnolitjlorae
The Magnoliiflorae here comprise mainly the woody members of the so-called
primitive dicotyledons. The following attributes are widespread, though lacking
in various members: primitive wood; P-type plastids in the sieve elements;
alternate exstipulate leaves ; cells with essential oils in leaves ; benzylisoquinoline
alkaloids present; tepals occasionally with tendency to trimery ; stamens flattened
and leaf-like with the microsporangia below the apex, pollen grains sulcate, 2nucleate; gynoecium apocarpous o r monocarpellate, endosperm formation
cellular. Nelumbo has been attached here rather than in the Ranunculiflorae, with
which its connection is probably not so strong; it is doubtless isolated and
possibly has evolved its herbaceous habit independently from the
Ranunculiflorae, even if its tricolpate pollen grains would be more in place in
this superorder.
The Nymphaezjlorae
This comprises the Piperales and Nymphaeales, the former is undoubtedly
also allied to the Magnoliiflorae. The most conspicuous feature of the
Nymphaeiflorae is the voluminous starchy perisperm, on top of which there is
still a well-defined endosperm tissue enclosing a small embryo. This represents an
organization which is unlikely to have evolved by convergence in independent
lines of evolution, especially when considering further concordant features in the
two orders, such as the S-type sieve tube plastids, the sulcate (or zonisulculate)
pollen grains and the similar leaves. Benzylisoquinoline alkaloids are rare in the
Piperales (but known in a single species of Piper) and apparently totally absent in
the Nymphaeales. In addition, leaves with essential oils are found in Piperales
but not in Nymphaeales. However, the latter order has evolved the capacity to
synthesize ellagitannins, otherwise unknown in this superorder, and absent in the
Magnoliiflorae and Ranunculiflorae. Piperales and Nymphaeales are no doubt
very different as a consequence of their adaptations to tropical rain forest and
aquatic habitats respectively. While the former has experienced a strong floral
reduction, some groups (especially Nymphaeaceae) have evolved large, diversified
and polymerous flowers. A tendency for floral trimery is found in both orders.
100
R. M . T. DAHLGREN
The Ranuncultjlorae
This superorder has certain features in common with the Magnoliiflorae, such
as the common presence of benzylisoquinoline alkaloids (here more complex)
and the frequent apocarpy, trimery and spiral organization of floral parts. A few
members have cellular endosperm formation. Few problems are involved in this
superorder, although family rank is applied most inconsistently to generic
groups in the Ranunculaceae-Berberidaceae region; families such as
Ciraesteraceae, Kingdoniaceae, Glaucidiaceae, Hydrastidaceae, Podophyllaceae and Nandinaceae being acknowledge by some authors but not by
others. The Papaverales are undisputably related to the Ranunculales.
The Caryophylhj7orae
This has been restricted to the order Caryophyllales, which is perhaps the
best studied of all orders with regard to the families and their interrelationships
(Mabry & Behnke, 1976). The order is easily defined by the characteristic P-type
sieve element plastids in combination with the well-developed, starchy perisperm
generally encircled by a curved embryo. Other common features are the presence
of betalains and saponins, the commonly aberrent secondary growth and the
frequently free, central placentation. By the exclusion of Batidaceae,
Gyrostemonaceae, Theligonaceae, Polygonaceae, Plumbaginaceae, Fouquieriaceae, Frankeniaceae, Elatinaceae, etc., the circumscription is now
clearcut.
The Polygoniflorae
The superorder comprises the order Polygonales which has long been
associated with Caryophyllales with which it shows several conspicuous
similarities. Some of these are superficial, others evolved by convergence (such as
the starchy seed) and some may express phylogenetic relationships. To the latter
category belong the amino acid sequence (Boulter, 1973) as well as shared
parasitic fungi (e.g., aecidia of grass rusts).
The Malvtjlorae
The Malviflorae (=Dilleniiflorae) are here very broadly conceived, and the
nine orders show affinity in different features. The order Cistales has here
been dissolved, since the Cistaceae show great resemblance in morphological,
anatomical, embryological, and chemical characters (also in flavonoids, cf:
Gornall, Bohm 8c Dahlgren, 1979) with families of the Malvales. They approach
closely the Bixaceae as well as the Cochlospermaceae, Tiliaceae and
Sterculiaceae. The Dilleniaceae are less clearly allied to the Malvales and form a
separate order, but agree to some extent with malvalean taxa so that a position in
this vicinity is justified. The genus Paeoniu, making up the Paeoniales, is placed
with some reservation in conjunction with Dilleniales. The close affinity between
the Malvales and Euphorbiales and the affinity between these and the Urticales
(Berg, 197 7 1 and Thymelaeales (Hegnauer, 197.3) is now becoming increasingly
clear. The order Rhamnales is here restricted to include Rhamnaceae only. I t was
acknowledged to be related to Euphorbiales by Thorne ( 1976) by virtue of several
features, among which should be mentioned the mucilage cells, the phloem, the
lepidote vesture, and some unusual peptide alkaloids. The Elaeagnales are no
ANGIOSPERM CLASSIFICATION
I 0I
doubt best treated in, or next to, this order, but the Plumbaginales have a more
uncertain position. The embryology including solitary anatropous ovules,
instability in embryo sac formation, and presence of an obturator may be taken
to support a euphorbiaceous affinity, while its seed coat structure is more similar
to that in the Rhamnaceae or Elaeagnaceae.
The Viollflorae
The Violiflorae consist of various orders with 2- or 3-carpellate gynoecia
having parietal placentation. A tendency for producing cyanogenic glucosides
or/and glucosinolates is apparent in some orders. Gynophores and
androgynophores are common. Ellagitannins are usually absent (except in the
Tamaricales), The position of Gyrostemonaceae and Batidaceae (two small
glucosinolate families mainly in the Southern Hemisphere) in Capparales is still
questionable but a certain affinity with Resedaceae seems. supported (Bolt
Jsrgensen, personal communication).
The Thelflorae
The Theales form a fairly homogeneous group of mostly woody plants,
frequently with scalariform perforation plates in the vessels, simple, entire and
coriaceous leaves, and choripetalous flowers with secondarily multistaminate
androecia. The ovules are mostly bitegmic and tenuinucellate, a fairly unusual
combination otherwise found mainly in the Primuliflorae among dicotyledons.
The Primullflorae
This group, consisting of the probably closely allied Ebenales and Primulales,
generally has actinomorphic and sympetalous flowers with central, sometimes
free placentation. The ovules are bitegmic and mostly tenuinucellate. The close
relationships of this group to other sympetalous groups have been much debated
but are dubious, as there are weak embryological and chemical bases for an
alignment to most of these groups. The chemical characters are more like those of
the Theales.
The Rosgorae
This superorder has been extended here to include the equivalent of the
Hamamelidiflorae and Saxifragiflorae (of Dahlgren, 197 5a). These complexes
are obviously allied through series of families. The trochodendralean end of this
complex by its primitive xylem, its cellular endosperm formation and apocarpy
are frequently associated with the magnoliiflorean complex (Endress, 1969) but
deviate from them in pollen morphology, chemistry and other details. There is
still some doubt about their mutual relationships and also about their affinity to
the Hamamelidales. The Hamamelidales combine features of the mainly insectpollinated Cunoniales-Rosales lines with the wind-pollinated Fagales, with
which they are undoubtedly related (Endress, 1977). The position of the
Myricales and Juglandales, which agree in many respects, has been interpreted
differently, mostly in favour of a fagalean but also of a sapindalean
(-anacardiaceous) relationship (Thorne, 1974). Recent serological indications
have been decisive in placing them next to Fagales (Fairbrothers and Peterson,
personal communications). Balanopales (= Balunops) is at present under in-
102
R. M . T.DAHLGREN
vestigation (Carlquist, personal communication). It has some features of the
Fagales, others of the Cunoniales, and might be best placed between these
orders.
The Podostemonzforae
Podostemonales (= Podostemonaceae sensu lato) are so specialized that they
cannot be associated with any other superorder without severe reservations. The
specialized habit and lack of endosperm formation are outstanding features.
These, in combination with the silica bodies, the frequently trimerous gynoecium
and fusion of stamen filaments could lead the imagination towards the orchids,
with which they have virtually no affinity (the seedlings for example being
typically dicotyledonous).
The FabiJorae
Although the order Fabales is often associated with the Rosales, its connection
with the Sapindales also seems to gain an increasing support through
morphological, palynological, anatomical, embryological and chemical evidence.
Thus the argument as to whether the Connaraceae should be placed with the
Fabales or with the Sapindales becomes less controversial when the orders are now
acknowledged as closely allied (and placed in close conjunction in a diagram).
The Proteijorae
There is little doubt that the disjunct Proteaceae is an old, isolated taxon. I t
is therefore placed in a separate order, Proteales, in its own superorder. As in the
Fabales, the pistil is monocarpellate and its solitary to several ovules have a
similar embryology. The chemical attributes, including flavonol derivatives,
leucoanthocyanins, arbutin and tannin accumulation agree better with a position
near the Fabales and the Rosales than in conjunction with the Santalales or the
Thymelaeales with which the Proteales have sometimes been associated.
The MyrtzJlorae
The Myrtales comprise a fairly natural group or perhaps two related groups of
families (Briggs & Johnson, 1979) which frequently possess opposite leaves,
rudimentary stipules, intraxylary phloem, tetramerous flowers with a
hypanthium, and two stamina1 whorls. The chemistry is related to that of the
Rosales, with which the Myrtales are perhaps the most closely allied. The
Haloragaceae and Rhizophoraceae senm strict0 deviate from the myrtalean
families to a variable extent and have a more uncertain position. However, their
position next to the Myrtales is likely, which explains their treatment here as
separate orders in this superorder.
The Rutzjlorae
This complex is one of the most variable in the angiosperms. In spite of this,
families in the six orders approach each other to such an extent that it is difficult
to draw clear borderlines. Thus, the Zygophyllaceae are sometimes placed in the
order Rutales, sometimes in Geraniales ; the Anacardiaceae are sometimes placed
in Rutales, sometimes in Sapindales. The flowers which are mostly choripetalous,
pentamerous and frequently obdiplostemonous and the frequent occurrence of
A N G I O S P E R M CLASSIFICATION
103
aromatic or resinous compounds are fairly typical. The two families of the
Tropaeolales are characterized by glucosinolates. The superficial similarity to
Balsaminaceae may or may not indicate relationship to this familv, and their
affinity to the Geraniales is also dubious.
The Santaltjorae
The order Celastrales in the present classification has been liberated from a
number of small families of uncertain affinity included there in Dahlgren
(1975a1, and now consists chiefly of the Celastraceae. Several attributes indicate
that this may be allied to the Sapindales (where in the future it may prove to be
more properly placed). Its long-acknowledged similarities to Vitidaceae and the
less advanced families of Celastrales (Olacaceae, Opiliaceae) justify the present
superorder. The Vitidaceae, by their combination of common attributes, are
difficult to place, and the problem has not decreased since Behnke (1974)
discovered that the sieve tube plastids are of the P-type. The Santalales no doubt
comprise a homogeneous group of families showing a successive reduction of
ovules, culminating in the Viscaceae and Loranthaceae. Polyacetylenes and
certain alkaloids also connect the santalalean families.
The Balanophoriflorae
As is the case among the semiparasitic taxa of the Santalales the wholly
parasitic Balanophorales (Balanophoriflorae) have undergone a strong ovular
reduction. Whereas the ovules of Cynomoriaceae are still unitegmic those of
Balanophoraceae are constantly ategmic and normally not well differentiated
from the inner tissue of the ovary, the climax being the extremelv small,
archegonium-like female flowers in Balanophora (Hansen, 1972). The affi’nities of
the Balanophorales are still totally unknown (as for the Podostemonales above).
Some have claimed that the Balanophoraceae and Cynomoriaceae are wholly
parasitic members of the Santalales, with which there are embryological
resemblances; other possible relatives are the Gunneraceae, o r possibly the
Ericales o r even the Asterales.
The AralizfEorae
By the common presence of resinous ducts, polyacetylenes and a similar basic
plan in the flower construction, this group is likely to form a n acceptable unit
(Hegnauer, 1969), but the circumscription of Pittosporales present some
problems. The core group of the Araliiflorae is the Araliales, with the closely
allied Araliaceae and Apiaceae recently united by Thorne (1973) to a single
family. A relationship of the Araliales to the Asterales is likely from their similar
basic floral construction, similar embryological features, 3-nucleate pollen grains,
exstipulate leaves, multilacunar leaf tr’aces, and possession of polyacetylenes and
sesquiterpene lactones.
The AsterzfEorae
On the whole the basic construction of the flowers in the Asterales and
Campanulales is similar and the orders exhibit parallel cases of pollen pump
mechanisms, parallel types of floral zygomorphy, etc. The chemical features are
variable in both orders but exhibit some similarities such as the ability to
104
R . M . T. DAHLGREN
form polyacetylenes but not iridoids. I t should be noted that the Campanulales as circumscribed here do not include Calyceraceae, Stylidiaceae or
Goodeniaceae, three families which have often, no doubt incorrectly, been
placed in Campanulales on the basis of superficial resemblance. They are now
placed in different positions in the Gentianiflorae-Corniflorae complexes, where
their inclusion involves no strain. As mentioned above, the Asterales also show
very strong similarities to the Araliales.
The SolanaJorae
The Solanales and Boraginales could probably be treated in the same order (cf:
Dahlgren, 1975a), although a subdivision is practical and easy, if based on the
ovules, which have their micropyle directed downwards (Solanales) and upwards
(Boraginales) respectively. The sympetaly and the unitegmic, usually
tenuinucellate ovules with cellular or nuclear endosperm formation are strongly
reminiscent of those in the Asteriflorae as well as those in the Lamiiflorae or
Gentianiflorae, but as far as is known, no taxa of the Solaniflorae possess the
polyacetylenes (or sequiterpene lactones) of the Asteriflorae nor the iridoids of
the Lamiiflorae or Gentianiflorae. Instead they produce a multitude of other
poisonous substances.
The CornEflorae
This complex is a variable one with unitegmic tenuinucellate ovules, cellular
endosperm formation, frequent sympetaly and possession of endosperm
haustoria as the most characteristic attributes. Many taxa form iridoid compounds, which are exclusively of carbocyclic types, except in the Sarraceniales, some Cornales and most Dipsacales, where secoiridoids are formed.
Most taxa of the Corniflorae are woody. The vessels, especially in Ericales
and Sarraceniales, may be primitive, with oblique end walls having scalariform perforation plates with numerous bars. The seeds may either be small
(many Ericales) or may have a small embryo in combination with copious endosperm, although in some Cornales and Dipsacales there is a tendency for the
endosperm to be consumed and for the embryo to increase in relative size. The
flowers also show a great variation. They are mostly pentamerous and haplo- to
obdiplostemonous, but a multiplication in the androecium has occurred in some
families (e.g., Actinidiaceae and Hydrangeaceae). The Fouquieriales in spite of
their probably bitegmic ovules have iridoids, ellagic acid, tricarpellate pistil, and
10 or more stamens and other attributes in which they agree with the CornalesEricales (Dahlgren et al., 19761, but not with the Solaniflorae next to which they
are sometimes placed.
The Loacijlorae
The Loasaceae in most classifications are placed in the Violales (Parietales),
where they are divergent especially in their embryologic features, the ovules
being unitegmic and tenuinucellate, the endosperm formation cellular, and
terminal endosperm haustoria present. Takhtajan ( 1969) placed the family near
Boraginaceae, which is more, but not wholly, satisfactory from this point of view.
The discovery of iridoids in Loasaceae points even more strongly to a position in
the region of the Corniflorae-Lamiflorae-Gentianiflorae,and also the recent
ANGIOSPERM CLASSIFICATION
I05
discovery o f secoiridoids, indicates a Cornalean-Dipsacalean o r Gentianiflorean affinity. Several genera of Loasaceae have haplostemonous androecia,
which is in better accord with the condition in the mentioned orders, although
these have sympetalous flowers whereas those in Loasaceae are choripetalalous.
This fact, in combination with a few attributes often found in the Violales, has
been decisive in placing the Loasaceae in a separate order and superorder.
The Gentiany7orae
The main part of the Gentianiflorae is made up of the Gentianales, which
include among other families the Rubiaceae. Some interesting though not
consistent attributes in this order are the opposite leaves, (interpetiolar) stipules,
intraxylary phloem, secoiridoids and, more rarely, indol and ipecac alkaloids.
The endosperm formation is also mostly nuclear in the Gentianales while it is
cellular in Oleales, Goodeniales and in the other superorders containing
iridoids. The orders of the Gentianiflorae show important similarities in many
features and contain secoiridoid producing plants. Thus the Oleaceae, for
example, are very similar to the Loganiaceae in many respects.
The Lamiy7orae
In contrast to the Gentianiflorae, the Lamiiflorae d o not form secoiridoids but
only carbocyclic iridoids, which are somewhat irregularly scattered through the
superorder. The flowers tend to be zygomorphic and are aggregated in racemose
inflorescences (thyrses, racemes, spikes, heads). As in the previous orders the
ovules are unitegmic, tenuinucellate and have cellular (rarely intermediate)
endosperm formation. In the Lamiales the fruit tends to be. a four-seeded
schizocarp as in (but independently ofl the Boraginales of the Solaniflorae. The
Hippuridales, and even more so the Hydrostachyales, are placed in Lamiiflorae
with reservations. The former is perhaps related to Plantaginaceae, and the
Hydrostachyaceae were also considered to be allied to this complex by JagerZurn (1965), but other conclusions based on the same data (see, for example,
Thorne, 1968) are that the Hydrostachyaceae approach Myrothamnaceae and
allied families in the Rosiflorae. Perhaps Gunneraceae should also be considered
as possible relatives of the Hydrostachyales.
The AlismatGorae
This superorder is easily circumscribed. I t is characterized by a number of
attributes which are otherwise unusual in monocotyledons : presence of
intravaginal squamules; absence of vessels in the stems (and often in the roots as
well); root hairs which are attached to particular, short epidermis cells;
amoeboid tapetum ; 3-nucleate pollen grains; apocarpy o r monocarpellate
gynoecia ; caryophyllad type of embryo formation, and absence of oxalate
raphides and silica bodies, etc. The Alismataceae are distinct from the other
families in several attributes, and make up the Alismatales, while the Zosterales
are more gradually attached to some Hydrocharitales. The Alismatiflorae are
probably most closely related to the Ariflorae.
The TriuridiJEorae
There is little doubt that the Triuridales are at least distantly related to the
Alismatiflorae but the closeness of the relationship is uncertain. The superorder
106
R. M . T. DAHLGREN
consists of chlorophyll-less saprophytes growing in tropical rainforests. The
flowers are small and unisexual, the female ones having numerous
monocarpellate, often subgynobasic pistils. This group differs from the
Alismatiflorae in the endospermous seeds; absence of parietal cells, and
periclinal divisions in the epidermis of the nucellus.
The ArtJlorae
Consisting of the Arales (Araceae and Lemnaceae) only, this is a well-defined
complex. I t is suprisingly similar to the Alismatiflorae in a number of concealed characters recalling the kind of similarity between the Piperales and
Nymphaeales. Such attributes are the vessel-less stem, amoeboid tapetum, and
the caryophyllad type of embryogeny. Typical of the Arales are the spadix
supported by a spathe; baccate fruits; tetracytic stomata; cellular endosperm
formation, and copious amounts of oxalate raphides; in all of which they are
different from the Alismatiflorae.
The Lilitjorae
The Liliiflorae comprise a considerable part of the monocotyledons including
for example the huge order Orchidales. Generally the stems are vessel-less ;buibs,
corms and rhizomes are common, though in different groups. Normally (but not
consistently) the flowers have two petaline tepal whorls, which may o r may not be
similar in shape and size. Septa1 nectaries or nectaries at the tepal base are found
in diverse groups, and the pollen grains are more often than not monosulcate.
The stomata are usually anomocytic, and certain orders have a starchy endosperm
(Bromeliales, Haemodorales, Velloziales, Pontederiales, Philydrales and
Typhales). In other classifications these are often associated with the
Commeliniflorae, and are transitional between for example the Commelinales in
that superorder and the Asparagales and Liliales of the Liliiflorae.
The Zingiberqorae
This superorder is well-defined by the combination of arillate and frequently
perispermous seeds, petiolate leaves, and a tendency for some of the stamen
homologues to be petaloid. The members with 5-6 functional stamens have
oxalate raphides and their seeds lack perisperm but have copious endosperm. In
these and many other attributes these families approach some liliiflorean orders
(Pontederiales, Bromeliales, Philydrales).
The CommelintJlorae
I n contrast to the Liliiflorae, this superorder shows adaptations to wind
pollination, and even those groups which are insect-pollinated, such as the
Commelinales, are difterent from the Liliiflorae, having, for example, sepaline
outer tepals. Most Commeliniflorae differ from the majority of the Liliiflorae in
characters such as the common occurrence of silica bodies, absence of oxalate
raphides, presence in stems of vessels with simple (and scalariform) perforation
plates, paracytic stomata, ulcerate pollen grains, starchy endosperm, absence of
steroid saponins and absence of chelidonic acid. Within the Commeliniflorae,
the Juncales-Cyperales, the Commelinales- Eriocaulales and the Poales
(including the Restionales) seem to form three fairly well-defined subgroups.
ANGIOSPERM CLASSIFICATION
107
The Areclflorae
This last superorder is retained in its classical strict circumscription, i.e., with
the exclusion of the Typhales and the Arales. The group consists of large herbs to
little-branched trees, the stems of which have n o secondary thickening growth, cf
some woody members of the Asparagales (of the Liliiflorae). The stomata are
largely tetracytic, silica bodies are frequently present, septa1 nectaries are
common (insect pollination is fairly wide-spread), the pollen grains are 3nucleate, the locules one-ovuled, the fruits drupaceous or baccate and the
endosperm generally non-starchy.
THE. DIAGRAM, POSSIBILITIES A N D LIMITATIONS
In the diagram of Fig. 1 the orders are illustrated as the transections of
branches of an imaginary evolutionary tree or hedge. The position of the orders
in relation to each other has been determined as far as possible by the degree of
similarity, reflecting the supposed phylogenetic relationships. In addition, the
depicted size of the orders is, to a reasonable degree, proportional to the number
of species included, but not strictly, because the area of the orders with one or
few species would then be too small to permit any shading or symbol to be
plotted in it.
As mentioned earlier (Dahlgren, 1975a: 122) such a framework in two
dimensions cannot possibly fulfil all requirements of juxaposition. An order,
when placed appropriately in relation to two o r three orders, is often not allowed
the desired proximity to a fourth order according to its similarities to
other orders. The juxapositions become self-explanatory when a sufficient
number of phylogenetically significant character states are followed in the
diagram, and this is why the distribution of some characters have been included
(Figs 3-7).
Despite the limitations of the diagram, it is useful in the following respects:
( 1 ) I t permits a quick and effective survey of the distribution of any mapped
attribute.
(2) I t permits effective comparisons between the distribution of two, o r several,
such attributes, whether these show great coincidence, are wholly or partly
exclusive, or, as in many cases, show other patterns.
(3) I t offers a chance to predict a yet-unknown character state in a species o f a
family from known characters in the neighbouring families, provided that
there is a clear tendency for aparticular state of this character to dominate in
the order (superorder).
(4)The diagram, when used for mapping character states considered as typical
to an order, may be used to test homogeneity. Each family consistently has a
definite area and position within the ordinal figure. Where the same family
deviates in several features from the other families this can quickly be
recognized as a spot of deviant shading in one diagram after another. Its
position then must be reconsidered.
( 5 ) As a result of comparison ofnumerous such diagrams, a deeper insight into
relationships between larger groups (orders, superorders) may be possible;
this diagram then serves as a kind of punch-card system with a common
matrix.
8
Figure 1 . The superorders of the angiosperms illustrated as clusters of orders in a two-dimensional frame-work. This diagram should be complemented with the following diagrams
in which the order names are given and with the linear list of orders and families in the text.
ANGIOSPERM CLASSIFICATION
I09
One of the limitations with the framework is that it is tempting to memorise it
as a factual constellation, while in fact, it serves as only one of several possible
ways of illustrating the ordinal relationships. Though superficially very different
from my diagram of 1975 (Dahlgren, 1975a1, this diagram depends on much the
same base material, and most of the main orders and superorders cohere in a
similar way. Both diagrams thus serve the same purpose although the latest
version is superior in many respects.
Many requirements must b e laid on a diagram of this sort in order to make
maximum use of it. There is obviously an upper tolerance limit for the
‘unnaturalness’ of its orders. For example, should the families of Scrophulariales
be intermingled with those of Gentianales, then characters like the pattern of
endosperm formation, types of iridoids, floral symmetry, etc. would give
confusing patterns - although by correlating the patterns of these characters it
might be possible to reconstruct the orders as circumscribed here.
Similar two-dimensional diagrams (Stebbins, 1974; Thorne, 1976, 1978, 1979,
in press) are capable of serving the same purpose.
The most severe limitation of the diagram is that false conclusions may be
drawn from individual features, or positions of orders in it. As was mentioned
above, for spatial reasons some orders come in closer conjunction with each
other than would be justified from an all-round comparison between them,
others are more distant than isjustified. This difficulty could be solved partly by
extending the figures for the orders as was done in Dahlgren, 1975a, for Saxifragales, Geratiales, Sapindales and Hamamelidales, but this method has been
avoided here, because the false conclusions of linear sequence were often drawn
for the families of these orders.
Complex patterns are difficult to illustrate with this, o r any other, method.
DISTRIBL‘TIONS OF SOME ATTRIBUTES IN T H E DIAGRAM
Only the distributions of a few attributes can be shown in this presentation,
and therefore some of the phylogenetically more significant ones have been
chosen, namely sympetaly (Fig. 21, unitegmic and ategmic ovules (Fig. 3 ) , the
occurrence of a parietal cell (Fig. 41, cellular and helobial endosperm formation
(Fig. 5) and some chemical characters : iridoids, polyacetylenes, glucosinolates
and benzylisoquinoline alkaloids (Fig. 6). In addition, for the monocotyledons,
further character states will be shown (Fig. 7).
As the distributions of these characters have been commented on elsewhere
(Dahlgren, 1975b; Nielsen et al., 1975; Dahlgren, 1977a, b ) only briefcomments
are given here.
Sympetalousflowers
Syrnpetalous flowers have long been recognized as significant in classifications
ever since pre-Linnean times. Most taxa with sympetalous flowers have been
classified in the ‘Monopetalae’, ‘Metachlamydeae’, ‘Sympetalae’ in various
of the classical works, and they have been grouped in the subclass ‘Asteridae’
by Cronquist (1968) and Takhtajan (1969). Because of the correlation in a great
many families between sympetaly, flowers with 5 sepals, 5 petals and 5 stamens in
alternating whorls, and a bicarpellate pistil, these families have been recognized
as a more o r less uniform group. This impression has been supported even more
Figure 2. Approximate distribution of sympetalous flowers in the dicotyledons (the monocotyledons are excluded in this survey as any comparison would be irrelevant). Fusion of
only some of the petals, as in Baslsaminaceae, Fabaceae smru stricto. Polygalaceae etc., is excluded. Problems arise where there are doubt of homology of the perianth, as in the
Santalalg where Loranthaceae is shaded but not Viscaceae. The perianths ofthe Thymelaeaceae and the Proteaceae are interpreted as homologous with the calyx in other plants.
Figure 3. Approximate distribution of u n i t e ~ p i c(dots) and a t e p i c (hatching) ovules. The great homogeneity of unite<pir ovuled groups in the right part of the diagram
(consisting of mainly the sympetalous groups) is obvious. Unitegmy has arisen along various other lines of evolution and has evolved in different W ~ V P
112
R. M. T. DAHLGREN
strongly by the concomittant possession of unitegmic, mostly tenuinucellate,
ovules and a generally cellular type of endosperm formation.
As will be shown below, some of the sympetalous groups are undoubtedly or
probably unrelated to the main part of these Sympetalae, for example, the
embryologically very aberrant Plumbaginales; the mostly bitegmic
Primuliflorae, which, in addition, normally have nuclear endosperm formation; certain Mimosaceae (Fabales); The Cucurbitaceae and the Caricaceae
(Violales), and many Crassulaceae (Saxifragales). The sympetalous
monocotyledons are not included in the diagram of Fig. 3.
Unitegmic ovules
Figure 4 shows the distribution of ovules with one integument, a supposedly
derived character state which no doubt has evolved along several evolutionary
lines, one (or possibly more) of which has grown to be large and diversified. This
coincides mainly with the Sympetalae complex, but also includes, for example,
some choripetalous taxa included here with some sympetalous ones in the
Corniflorae (comprising Ericales, Sarraceniales, Cornales, Dipsacales and
Eucommiales). As will be shown below, the close mutual connection between the
families included in Corniflorae and the relationships between these and the
main part of‘ the Sympetalae is supported by other embryological properties
( Philipson, 1974). Besides, the relationships between them and the Loasiflorae,
Gentianiflorae and Lamiiflorae is supported by their contents of iridoids (see
below).
However, unitegmic ovules have also evolved in widely different and independent lines of evolution, among which should be mentioned many Fagales and
all Juglandales and Myricales (the latter two orders being undoubtedly closely
interrelated), also certain genera of Rosaceae, certain genera of Ranunculaceae
(Bauman 8c Calis, 19771, Pepermia and related genera (‘Perperomiaceae’) of
Piperaceae, most taxa of Salicaceae, the Sapotaceae, etc. Isolated genera with
unitegmic ovules are further known in several other families. Possibly related to
the Sympetalae are such groups as the Santalales and/or Balanophorales where
the ovules are subjected to more or less strong reductions.
Presence of parietal cells
The dicotyledonous groups without parietal cells (‘tenuinucellate’ ovules in
the sense of Dahlgren, 1975b) again include most of the Sympetalae, including
the ericalean and most cornalean families. Further, some dubiously related
sympetalous groups lack parietal cells, such as most Primuluflorae. Besides,
parietal cells are lacking in groups probably very distantly related to the
Sympetalae, including most Theales and Droserales ; the Podostemonales ; some
Geraniales (Oxalidaceae, Linaceae), all Tropaeolales and Balsamhales, and
certain Celastrales. In monocotyledons, a parietal cell is lacking in the ovules of
all the Orchidales, Burmanniales and Triuridales. It is also absent in the Poales
and many Eriocaulales, Liliales, Asparagales and Velloziales.
Endosperm formation
Adding to the phylogenetic significance of the correlation between sympetaly
and the two embryological characters previously mentioned is the distribution of
dif‘ferent types of endosperm formation (Fig. 5). The ab initio cellular type is
Figure 4. Approximate distribution ofovules with and without a parietal cell in the angiosperms (unshaded and shaded respectively). Explanation is given in the text. Absence 01
parietal cells in dicotyledons partly coincides with the occurrence of one integument and is no doubt a derived character state. Groups with this attribute doubtless have evolved
along various lines of evolution, one or a few main ones coinciding with the main sympetalous section.
w
--
Figure 5.Approximate distribution of the cellular (dots), helobial (vertical hatching) and intermediate (oblique hatching) types of endosperm formation in angiosperms. Unshaded
areas represent the nuclear type plus unknown groups. Here the cellular type, represented in most Magnoliiflorae may well be the primitive state. Again, we find a concentration of
one character state (the cellular type) in the ‘Sympetalae’, although, characteristically, it has broken down partly in the Asterales, Solanales and Boraginales and almost completely
in the Gentianales.
ANGIOCPEKM CLASSIFICATION
115
concentrated in the Sympetalae, especially in the four iridoid-containing
superorders Corniflorae, Lamiiflorae, Loasiflorae and Gentianiflorae (excepting
the Gentianales in which endosperm formation largely has gone over to the ab
initio nuclear type). The variability in endosperm formation in the Asterales of the
Asteriflorae and the Solaniflorae is noteworthy, but the original type is probably
the cellular type in these groups too. In addition, this type is found in
Balanophorales, most Santalales, some Celastrales, and scattered members o f
the Rosiflorae sensu lato, the latter including Gunnerales, many Saxifragales,
many Buxales, some Hamamelidales and the Trochodendrales.
Further, in the dicotyledons, the cellular endosperm formation is found in
many Magnoliiflorae and Nymphaeiflorae and some Ranunculiflorae. This
pattern of distribution is doubtless of great phylogenetic interest in regard to the
Sympetalae and related groups. On the basis of the common presence of cellular
endosperm formation in these undoubtedly advanced plants, this character state
is usually considered to be derived, but this is contradicted by the fact that the
cellular type of endosperm formation is widespread in the Magnoliiflorae and
Nymphaeiflorae. The fact that it is also found in the Trochodendrales, which are
primitive in several respects, likewise supports the impression that the cellular
type can be interpreted as primitive, and may have been retained in some
evolutionary lines including the Sympetalae and others mentioned.
In monocotyledons, the ab initio cellular endosperm is largely restricted to the
Arales, but it is uncertain whether it is primitive here o r not. The helobial
endosperm formation is mainly restricted to the monocotyledons, and has its
main distribution in the Alismatiflorae, the capsule-fruited Asparagales, the
liliiflorous orders with starchy endosperm, the Zingiberales, the Juncales and the
Cyclanthales.
Most other monocotyledons have nuclear endosperm formation.
Some chemical compounds
Chemical characteristics can further elucidate the relationships, especially
between the sympetalous taxa of the dicotyledons.
IRIDOIDS comprise a group of chemical compounds which frequently serve as
‘bitter principles’ in plants, making these unpleasant to browsing and egg-laying
animals. Their distribution is shown in Fig. 6 . While they are widely distributed
in the Corniflorae, Loasiflorae, Lamiiflorae and Gentianiflorae, they are totally
unknown in the Araliiflorae, Asteriflorae and Solaniflorae. Further, with the
exception of four known genera (Liquidambar, Daphniphyllum, Xylocarpus,
Fouquieria) they are entirely restricted to taxa with one integument. Their
widespread distribution among the families in the four superorders suggests that
they may have evolved early in their common ancestry. It is as yet difficult to
interpret the odd occurrence of iridoids in the four genera outside these main
groups; independent evolution in all o r in some of them must not be excluded.
POLYACETYLENES (Fig. 7 ) are largely vicarious in relation to the iridoids in the
Sympetalae and their relatives, being found in the Asteriflorae, the probably
quite closely related Araliiflorae, and in the Santaliflorae; otherwise, they are
known only in very scattered genera (within the Rutales, Malvales, Laurales and
Goodeniales). The discovery of polyacetylenes in the Simaroubaceae of the
Rutales may have some significance.
Figure 6. Approximate distribution of certain groups of chemical compounds in angiosperms: iridoids (sparse dots), polyacetylenes (oblique hatching), glucosinolates (vertical
hatching), and benzylisoquinolinealkaloids (dense dots). Comments are given in the text.
,I'VGI O S P E R M CLASSIFICATION
Figurc 7 . Appr-oximdtc distribution of A, oxalate raphides and B, silica bodies
monocotvledons.
in
thr
The peculiar distribution of iridoids and of polyacetylenes may suggest either a
possible bifurcation in the past evolution of the pro-Sympetalae o r a biphyletic
origin of them. The Solaniflorae, which lack iridoids as well as polyacetylenes,
may represent a separate evolutionary branch, o r may have been connected to
118
R. M. T. DAHLGREN
either of the other main groups, eventually having lost the ability to synthesize
the characteristic compounds.
The GLUCOSINOLATE or isothiocyanate plants include members of the orders
Capparales (Brassicaceae, Capparaceae, Tovariaceae, Resedaceae, Moringaceae,
Gyrostemonaceae and Batidaceae), Salvadorales (Salvadoraceae), Violales
(Caricaceae), Euphorbiales (Drypetes of the Euphorbiaceae), Tropaeolales
(Tropaeolaceae and Limnanthaceae) and perhaps Sapindales (Bretschneideraceae). There are still great doubts about the significance of glucosinolates. They comprise very diverse groups of compounds and may have evolved
along several lines of evolution.
Finally, the BENZYLISOQUINOLINE ALKALOIDS should be mentioned. They
have their greatest concentration in the Magnoliiflorae and Ranunculiflorae,
which are now generally believed to be related. However, they may be lacking in
some magnoliiflorean families, such as Myristicaceae, Winteraceae, Illiciaceae and
Schisandraceae, and several small families, not yet investigated. Further, they are
unknown in all Nymphaeales and most Piperales, being so far known only in
some species of Piper. In the Ranunculiflorae the benzylisoquinoline alkaloids
are more complex than in the Magnoliiflorae, especially so in the Papaverales;
but they are absent in part of Ranunculaceae and Berberidaceae (e.g., in
Podophyllum) and not known in the Sargentodoxaceae or Lardizabalaceae,
although they are plentiful in the Menispermaceae. The occurrence of complex
benzylisoquinoline alkaloids in a few Rutaceae has been regarded as expressing
relationships with the Ranunculiflorae, while their occurrence in other groups,
(e.g., in some Rhamnaceae, members of the Buxaceae and Symplocaceae, Croton
in the Euphorbiaceae) has not been considered to have any phylogenetic
meaning.
THE MONOCOTYLEDONS
In the course of 1978 and 1979 the distribution of numerous attributes in the
monocotoyledons has been studied more intensively in Copenhagen (Dahlgren &
Clifford, in press). In the angiosperm classification presented here, the
monocotyledons have been classified on the basis of these results. A separate
diagram for monocotyledons has been used in Fig. 7 to illustrate the distribution
of a few attributes in these.
I t seems that the classification of the monocotyledons does not present such
great difficulties as that of the dicotyledons, although there are disagreements in
finding an appropriate level when handling the Liliiflorae families.
In the classificatory list the aim has been to circumscribe the families as
naturally and homogeneously as possible. The opposite attitude would be to
include most monocotyledons with two hypogynous petaline perianth whorls
and two whorls of stamens in a giant Liliaceae smu lato. Such a concept would
indeed represent a heterogeneous group and its maintenance deserves little
support. An intermediary approach might cluster together the segregate groups
of the Liliiflorae into somewhat larger families as follows :
DIOSCOREALES: Dioscoreaceae (including Stenomeridaceae and Trichopodaceae), Taccaceae, Stemonaceae (including Croomiaceae), Trilliaceae
ASPARACALES: Philesiaceae (including Luzuriagaceae and Geitonoplesiaceae),
Smilacaceae (including R'ipogonaceae and Petermanniaceae), Convallariaceae
/i1\1 L I 0 s PERM CLASS1 FICATIO N
I19
(including Asparagaceae, Ruscaceae and Hereriaceae), Dracaenaceae
(including Nolinaceae), Doryanthaceae, Dasypogonaceae, Xanthorrhoeaceae,
Agavaceae, Hypoxidaceae, Tecophilaeaceae, Cyanastraceae, Asphodelaceae
(priority dubious; including Phomiaceae, Dianellaceae, Eriospermataceae,
Asteliaceae, Aphyllanthaceae, Anthericaceae and Aloeaceae), Hanguanaceae,
Hemerocallidaceae, Funkiaceae, Hyacinthaceae, (including Agapanthaceae
and Gilliesiaceae),Amaryllidaceae
LILIALES: Iridaceae, Geosiridaceae, Alstroemeriaceae, Colchicaceae, Liliaceae
(including Tricyrtidaceae and Calochortaceae), Melanthiaceae
BURMANNIALES : Burmanniaceae (including Thismiaceae),Corsiaceae
ORCHIDALES: Apostasiaceae, Orchidaceae (includingCypripediaceae)
TYPHALES: Typhaceae (includingSparganiaceae)
(0ther liliflorous orders are monofamilial.)
This classification, however tempting, camouflages the great distinctness of
many groups of genera (especially those placed here in Asphodelaceae ~ e n mlato)
and even this semi-lumping approach is therefore discouraged here, as it would
also be by, for example, Huber (1969, 19771, who has spent much effort in the
study of the Liliiflorae.
Many attributes have a phylogenetically significant distribution in the
monocotyledons and may be useful in the main grouping. Among these only
two will be chosen here, namely the distributions of oxalate raphides and of silica
bodies. These both contribute in demonstrating a basic division between the
commeliniflorean and the liliiflorean complexes (to the left and right respectively
in the monocotyledon diagram).
OXALATE RAPHIDES are wide-spread in the Liliiflorae but seem to be absent in
most or all Commeliniflorae as here defined. It is noteworthy that raphides are
also present in the Areciflorae and Ariflorae but lacking in the Alismatiflorae and
Triuridiflorae complexes, while in the Zingiberiflorae they are restricted to the
taxa with 5-6 anthers.
SILICA BODIES show a more complicated distribution pattern, being mainly
concentrated in the Commeliniflorae, the Zingiberiflorae, and at least the
Arecales of the Areciflorae. However, there are silica bodies in the Bromeliales
and many tropical orchids (Orchidales) among the Liliiflorae as circumscribed
here. In order to evaluate this feature, the shape and size of the silica bodies, and
also the position in the tissues of the cells containing them must be taken into
consideration. There is little doubt that silica bodies have appeared in separate
lines of evolution, as is indicated by their totally different shape in the Poales and
the Cyperales. They are mostly lacking in the Juncales which are closely related to
the Cyperales and in some other respects have a more basic organization. In the
Cyperales they generally form conical bodies with the tips of the cones directed
outwards, while in grasses they have various, but not conical, shapes.
By considering the distribution of numerous such attributes, a more profound
knowledge of connections between taxonomic groups of higher categories may
be possible.
PROSPECTIVES, RELATION T O A FEW O T H E R CURRENT CLASSIFICATIONS
There is a tendency at present for the current systems of classification of
angiosperms to approach one another. Insufficiencies have become obvious and
R. M . T. D A H L G R E N
120
have been emended. Intensive studies result in clarification, as with the position
ot‘ Theligonum (Wunderlich, 1972).
The systems of Takhtajan (19691, Cronquist (1968, 1979) and Thorne (1976)
are at present under revision. The last version of Takhtajan’s diagram may be
that shown in Jones 8c Luchsinger (19791, but a fuller version is soon to be
published in the Botanical Review (Cronquist, personal communication).
Takhtajan (19691, like Cronquist (19681, uses the subclass level as an
intermediate rank above the order and superorders. In the monocotyledons, the
Arales and Typhales are associated with the Arecales, Pandanales and
Cyclanthales to form the Arecidae. In the present classification the former two
orders are not allied to the latter three nor are they allied with each other. With
certain exceptions the main grouping of the monocotyledons is otherwise in
good agreement with the present system. In the dicotyledons the subclass
Magnoliidae largely corresponds to the Magnolianae and Nymphaeanae of the
present classification. A closer association between the Piperales and
Nymphaeales is here supported by the similarity of seed. In the Ranunculidae of
Takhtajan (1967) the Sarraceniales no doubt form an alien element and would be
better associated with Ericales or Cornales (Dahlgren, 1975a; Jensen et al., 1975).
In Takhtajan’s Caryophyllidae there are doubts about the affinity between the
three orders Caryophyllales, Polygonales and Plumbaginales. The Urticales in
Takhtajan’s system are associated with the Hamamelidae, while most modern
data seem to support a connection with the Malvales-Euphorbiales-Thymelaeales lines treated by Takhtajan in the Dilleniidae. It seems questionable
that the Hamamelidales should appear in so remote a position from the RosalesSaxifragales line of the Rosidae. The Dilleniidae in Takhtajan’s classification
include the order Ericales, which is thus shown as an evolutionary branch very
distant from the Cornales. This is not supported by embryological and chemical
data and is a weak point shared also by the systems of Cronquist and Thorne.
Further points to be mentioned are the association of the Nepenthales and
Elaeagnales with Saxifragales and the close association of the Araliales with the
Cornales, which is again not supported by embryological and chemical
characters. Furthermore, the Araliales are very remote from the Asterales (and
Campanulales) in Takhtajan’s system, which is not in accord with recent chemical
Hegnauer, 1964). Otherwise, most groups of the iridoid plants
and other data
(except Ericales and Cornales) are fairly closely placed, although interrupted by
the iridoidless Polemoniales.
In its main features the latest version of Cronquist’s system (Cron uist, 1979;
diagram in Jones 8c Luchsinger, 1979) is very reminiscent of that o Takhtajan
( 1969) and recognizes the same subclasses, although the Ranunculidae are
included in the Magnoliidae; an additional superorder was recently erected in
the monocotyledons, namely the Zingiberidae (comprising the Bromeliales and
Zingiberales). Among the Commelinidae the Cyperales include the grasses
(Poaceae) as well as the Cyperaceae which contradicts morphological,
cytological, anatomical and other evidence. The inclusion of Typhales in
Commelinidae is in accord with most attributes of this order, although the wind
pollination syndrome responsible for this may have evolved independently.
The Magnoliidae correspond to the Magnoliiflorae, Nymphaeiflorae and
Ranunculiflorae of the present classification. The Piperales and Nymphaeales are
more remote from each other (see above) than might seem justified from seed
(CJ:
9-
\ Z ( , I O 5 P F , K M CLASSIFICATIO‘V
121
construction. The Caryophyllidae have the same circumscription as in Takhtajan’s
system and basically so have the Hamamelidae, although the small groups
Eucornmiales, Didymelales, Leitneriales and Daphniphyllales form separate
orders within this superorder in the Cronquist classification. The Dilleniidae,
with the core group Theales in Cronquist’s system also include the Ericales (and
Diapensiales) which are thus placed far from the Cornales. The Nepenthales are
associated with the Theales in Cronquist’s system, as in the present classification,
but include the Sarraceniaceae, the latter no doubt an alien element (though
close to the Ericales). The Rosidae in Cronquist’s system show less connection
with the Dilleniidae than in Takhtajan’s system but contain essentially the same
orders. The Euphorbiales are associated with Celastrales in Cronquist’s Rosidae,
which is probably less desirable than their association with MahalesThymelaeales d5 in Takhtajan’s system. The Apiales (= Araliales) in Cronquist’s
Rosidae are connected with the Sapindales but not (as in Takhtajan’s system) with
Cornales, which are placed in the same subclass; the remote position of the
Apiales and Asterales is thus a common feature of both classifications. The
Gentianales (separate from Rubiales) have a basic position in Cronquist’s
Asteridae where they separate the Asterales from the Campanulales, each of
which being connected with various iridoid-containing orders. From a
chemotaxonornic point of view this seems unwarranted. The iridoidless
Solanales are in the midst of a number of iridoid orders, which comprise the
Lamiiflorae in the present classification.
In addition to the division of the angiosperms into 11 subclasses, which is
common to the Takhtajan and Cronquist systems, both diagrams give the
impression that extant orders are evolved from each other, although the
angiosperms of Cronquist’s system are ultimately rooted in hypothetical
‘proangiosperms’.
The classificatory diagram of Thorne (1979) published as a separate chart,
differs only slightly from a previous version (Thorne, 19781, likewise published
separately at first but later published in Jones & Luchsinger (1979: 362). The
superorders in this diagram radiate from an empty centre representing extinct protoangiosperms. As in the present classification, the superorders are
more numerous than Takhtajan’s and Cronquist’s subclasses. The monocotyledon consist of the Commeliniflorae, Ariflorae, Typhiflorae, Areciflorae, Alismatiflorae, Triuridiflorae and Liliiflorae, the first and last mentioned
of these being separated from each other by the other orders. This is unfortunate
considering the close connections between the Liliiflorae with starchy endosperm (Velloziaceae, Haemodoraceae) and the Philydraceae, Bromeliaceae
etc. placed in Thorne’s Commeliniiflorae. The Zingiberales are included in the
Commeliniflorae, joining up with the suborders Bromeliinae- Ponterderiineae
(-Commelinineae) of the Commelinales, which is in good agreement
with the views held here although the Bromehneae and Pontederiineae form
separate orders of my Liliiflorae. The Chenopodiiflorae in Thorne’s system of
1979 are liberated from the Polygonales and Plumbaginales and thus are well
defined, while the Theiflorae is the more extensive, including the Ericales,
Primulales (with Plumbaginaceae), Polygonales and Ebenales. The Ericales and
Sarraceniaceae (included in the Theales) thus are widely separated from the taxa of
Cornales as circumscribed here. Thorne does not pay any attention to the
correlation between the embryological attributes and iridoids as outlined above
122
R . M . T. DAHLGREN
(they are not considered by Takhtajan or Cronquist either) and the families of the
Corniflorae, Loasiflorae, Gentianiflorae and Lamiiflorae are therefore scattered
in his diagram, which for this reason appears to be unnatural in some sections.
However, the Oleales have been placed in conjunction with the Gentianales, and
the last classification (Thorne, 1979) shows the Solanales-Campanulales
(Solaniflorae)in close conjunction with the Asteriflorae, which is also approached
by the Araliales, all this being in accord with recent findings. Chemotaxonomically
and embryologically unnatural units are the Corniflorae in Thorne’s system which
consist of the Araliales, Dipsacales and Cornales, the last-mentioned of which
include Vitaceae.
According to some evidence, the Solanales of Thorne’s superorder
Solaniflorae agree better with the Boraginales (of Thorne’s Lamiiflorae) than
with Campanulales with which they are associated by Thorne. The Lamiales,
which are associated with the Boraginales in Thorne’s Lamiiflorae, would also
match better with the Bignoniales of his Gentianiflorae, where Bignoniales are
placed together with Gentianales-Oleales. Fabaceae Jemu luto is treated in the
suborder Fabineae together with the Sapindineae and Rutineae in Thorne’s
Rutiflorae. This is a radical step which gains support from various sources.
On a whole, the classifications of Thorne (1969- 1979) are characterized by
fewer and more widely circumscribed orders than in the present system. However,
the orders are frequently divided into several suborders. The families are likewise
relatively widely circumscribed, but often divided into fairly distinct subfamilies.
The hierarchy thus established is somewhat heavier than in other contemporary
systems, but allows a more modulated picture of interrelationships.
In nomenclatural construction the classification presented here agrees best
with that of Thorne, as the subclass level has been reserved for the mono- and
dicotyledons, and the superorder level has been widely exploited. The
superorders of the classifications are also of comparable number and size to
those in Thorne’s classification and I have adopted his nomenclatural construction, using the termination --orae for the superorders. This ending has been
extensively used for a long time, especially for some groups of orders, e.g., the
Liliiflorae and Rosiflorae.
It is to be hoped that some decisions of a purely nomenclatural character and
of rank can be taken in order to give the current classifications (at least
superficially) a more comparable appearance. Divergent philosophy, and the interpretation and different use of factual information will inevitably continue to
give each classification individual features, and it would be wrong to violate
sound conclusions merely in order to achieve an increased correspondence
between the different classifications.
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