Acta Botanica Sinica
植 物 学 报
2004, 46 (9): 1075－1082
http://www.chineseplantscience.com
Female Cone Development in Fokienia, Cupressus, Chamaecyparis
and Juniperus (Cupressaceae)
ZHANG Quan1, 2, Sodmergen1, HU Yu-Shi2, LIN Jin-Xing2*
(1. College of Life Sciences, Peking University, Beijing 100871, China;
2. Institute of Botany, The Chinese Academy of Sciences, Beijing 100093, China)
Abstract: The ontogeny and vascular systems of female cones of the Fokienia, Cupressus, Chamaecyparis
and Juniperus were investigated in detail using scanning electron microscopy (SEM) and conventional light
microscopy. In the species examined, in the axils of the bracts, the first recognizable structure was a broad
meristematic swelling, from which ovules developed. No ovuliferous scales developed during the ontogeny
of the female cones. The number of ovules and ovule developing sequence displayed considerable variation
in different species. However, development of the bracts was similar in all of the investigated species.
Following pollination, the foliage-like bracts became peltate bract scales due to intercalary expansion, and
global cones formed. In addition, the vascular system in the bract scales became intricate, and inverted
vascular bundles emerged in the adaxial of the mature bracts. Based on these observations, a morphological
interpretation and possible evolutionary trend of the Cupressaceae female reproductive structures was
discussed.
Key words: Cupressaceae; female cone development
The female cone of conifers has received considerable
attention, not only for its systematic significance (Li, 1953;
Hart and Price, 1990; Fu et al., 1999; Gadek et al., 2000), but
also for its intriguing morphology (Florin, 1954; Farjon and
Garcia, 2003; Schulz et al., 2003). In a series of detailed
studies of fossil and living conifers, Florin (1954) came to
the widely accepted conclusion that the female cones of
most conifers are compound structures in which the
ovuliferous scale represents a modified branch borne in
the axil of a bract scale. Many scientists initially believed
that, in the Cupressaceae, the ovuliferous scale and bract
scale were completely fused (Sporne, 1971; Owens and
Molder, 1980; Gifford and Foster, 1989; Page, 1990).
However, subsequent studies have shown that, in female
cones of certain genera, no ovuliferous scale develops
(Takaso and Tomlinson, 1989; Zhang et al., 2000; 2001;
Tomlinson and Takaso, 2002). These results imply that there
must be an alternative explanation of the morphological
nature of the female reproductive structures in the
Cupressaceae. In the present study, we examined female
cone development in the Chamaecyparis, Cupressus,
Fokienia and Juniperus genera, as part of a series of studies on conifer female reproductive structures (Hu et al.,
1989; Napp-Zinn and Hu, 1989; Shi and Wang, 1989; Wang
et al., 1995; Lin and Hu, 2000). The overall aim is to deter-
mine the morphological nature and evolutionary trends of
conifer female reproductive structures, with reference to
other studies on the ontogeny of female cones.
1 Materials and Methods
Female cones of Juniperus chinensis Linnaeus and
Chamaecyparis pisifera (Siebold and Zuccarini) Endlicher
were collected in the Beijing Botanical Garden, Institute of
Botany, The Chinese Academy of Sciences. Cones of other
species, such as Cupressus duclouxiana Hickel,
Cupressus funebris Endlichler, Cupressus torulosa D. Don,
Chamaecyparis lawsoniana (A. Murray bis) Parlatore,
Fokienia hodginsii (Dunn) A. Henry and H. H. Thomas,
Juniperus recurva var. coxii (A. B. Jackson) Melville, J.
gaussenii W. C. Cheng, were collected in the Kunming
Botanical Garden, Kunming, Yunnan. All collections were
made throughout the annual cycle from mature plants.
Materials were fixed in FAA (formalin-acetic acid-alcohol).
For scanning electron microscopy (SEM) observation,
the fixed young seed cones were dehydrated and dissected
in a graded alcohol series, critical-point dried and coated
with gold palladium. Specimens were observed under a
Hitachi S-800 scanning electron microscope operated at
30 kV.
For histology and vascular analysis, fixed cone samples
Received 9 Mar. 2004 Accepted 21 Jun. 2004
Supported by the Knowlege Innovation Program of The Chinese Academy of Sciences (KSCXZ-SW-108) and the National Science Fund of
China for Distinguished Young Scholars (30225005).
* Author for correspondence. Tel: +86 (0)10 62591431 ext. 6211; Fax: +86 (0)10 62616340; E-mail: <[email protected]>.
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collected one month before pollination, at the pollination
stage, and near maturity, were prepared for paraffin
sectioning. Serial longitudinal and transverse sections at
8－12 µm thickness were cut and stained in hematoxylin
and safranin.
2
Results
2.1 Female cone development in Fokienia
There is only one species in the genus Fokienia, F.
hodginsii. The female cone of this species consists of six
to nine pairs of decussate bracts, initiated on the terminal
branchlet in early September. In the axils of each fertile
bract in the middle of the cone, two ovule primordia were
observed to initiate (Fig.1a). The ovule developed in a
distinct acropetal manner (Fig.1b). When all structures of
the cone had been established, there were, at most, 28
ovules formed along the long axis of the cone (Fig.1c).
However, only four to eight ovules and subtending bracts
in the middle of the cone were fully developed after
pollination. Two or three pairs of the bracts in the middle
of the cone developed into a peltate scale, and the cone
assumed a globular shape. The other ovules were aborted,
with the subtending bracts remaining poorly developed
(Fig.2).
The development of the vascular system of the F.
hodginsii young cone up to the time of pollination was
Fig.1. Scanning electron microscopy (SEM) photographs of dissected female cones of Fokienia hodginsii at successive stages of
development. a. Ovule primordia initiated. b. Ovules developed in an acropetal manner. c. A cone with all ovules fully developed. Bar
= 200 µm. Abbreviations: B, removed bract; O, ovule; OP, ovule primordia.
Fig.2. Diagrammatic longitudinal sections of Fokienia hodginsii
cones at different developmental stages. a. Ovules initiated in an
acropetal manner. b. Bracts opened at the time of pollination. c.
Bracts developed into peltate scales and vascular system become intricate in mature cone. B, bract; O, ovule; S, seed; V,
vascular. Dotted lines indicate the vascular bundles that had
developed after pollination.
ZHANG Quan et al.: Female Cone Development in Fokienia, Cupressus, Chamaecyparis and Juniperus (Cupressaceae)
very similar to that of the vegetative shoot. Each bract
contained a single centrally situated vascular bundle. During the intercalary growth of the bract following
pollination, the vascular system in the female cone developed into an intricate pattern. At the base of the bract
scale, apart from the central trace, two lateral bundles diverged from the cone axis, and each bundle immediately
branched into several bundles, forming two series that
branched into the abaxial and adaxial sides of the bract
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scale. The adaxial series of bundles were inverted, with the
xylem on the abaxial side and the phloem on the adaxial
side (Fig. 2c; Fig. 6a).
All of the species investigated in this study displayed
similar vascular development pattern in the cone.
2.2 Female cone development in Cupressus
The genus Cupressus contains about 17 species, of
which three were examined: C. funebris, C. duclouxiana
and C. torulosa. Female cones of these species were found
Fig.3. Scanning electron microscopy (SEM) photographs of dissected female cones from Cupressus funebris (a－c), Cupressus
duclouxiana (d－f) and Cupressus torulosa (g－i). a, d, g. The broad meristematic swelling (arrows) formed in the axil of the bract. b,
e, h. Ovule primordia initiated. Numbers indicate the order of ovule initiation. c, f, i. Cones with all ovules developed. Bar = 200 µm.
Abbreviations: B, removed bract; I, integument; N, nucellus; O, ovule; OP, ovule primordia.
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to have numerous ovules and a similar developmental
pattern.
The C. funebris female cone initiated in early July and
had three to five pairs of bracts by the end of the month. In
the axil of each bract, a broad swelling was observed (Fig.
3a), on which two series of ovules were produced in basipetal order. The first series contained three ovule primordia,
and the second series with two ovule primordia appeared
later and alternated with the first series (Fig.3b). Multiple
ovules clustered between the bracts, obscuring the relationships between the ovules and the subtending bracts
(Fig.3c). No ovule developed in the axils of the uppermost
pairs of bracts (Fig.3b, 3c).
Ovules development in C. duclouxiana (Fig.3d－f) and
C. torulosa (Fig.3g－i) cones were similar to that of C.
funebris except that several ovules initiated at the axils of
the uppermost bracts.
2.3 Female cone development in Chamaecyparis
Six species of the Chamaecyparis genus occur in East
Asia and North America, and we examined two of these
species, Ch. lawsoniana and Ch. pisifera. In mid-July, a
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subset of the vegetative buds of Ch. lawsoniana developed into female reproductive buds. The newly formed
female cone contained four to six pairs of bracts. Ovule
primordia initiated simultaneously in the axils of two or
three pairs of bracts in the middle of the cone (Fig.4a－c).
Generally, two or four ovules developed in the axil of each
fertile bract. In the bracts containing four ovules, the lateral two ovules initiated later than the two middle ovules.
Abortion of the middle two ovule primordia was observed
(Fig.4c).
The ontogeny of the Ch. pisifera female cone was similar to that of Ch. lawsoniana, except that the axil of each
fertile bract always generated two ovules (Fig.4d－f).
2.4 Female cone development in Juniperus
Of the approximately 60 species in the Juniperus genus,
we investigated three species: J. chinensis, J. gaussenii,
and J. recurva var. coxii. The female cone of J. chinensis
consisted of three pairs of bracts whose arrangement followed that of the leaves in a decussate manner. In July, the
first distinguishable structure in the axil of each bract in
the middle of the cone was a broad meristematic swelling
Fig.4. Scanning electron microscopy (SEM) photographs of dissected female cones of Chamaecyparis lawsoniana (a－c) and
Chamaecyparis pisifera (d－f). a. Ovule primordia initiated. b. All ovules developed in a cone. c. Two ovule primordial (fat arrows) that
failed to develop into ovules. d. The broad meristematic swelling (arrow) formed in the axil of the bract. e. Nucellus and integument
developed. f. A cone with all ovules developed. Bar = 200 µm. Abbreviations: B, removed bract; I, integument; N, nucellus; O, ovule;
OP, ovule primordia.
ZHANG Quan et al.: Female Cone Development in Fokienia, Cupressus, Chamaecyparis and Juniperus (Cupressaceae)
(Fig.5a), on which two ovule primordia initiated (Fig.5b). A
typical female cone of J. chinensis consisted of two pairs
of decussate bracts with two ovules in the axil of each of
the lower bracts (Fig.5c).
J. gaussenii female cones had two or three pairs of
decussate bracts at the ends of very short branchlets. In
general, a typical female cone of J. gaussenii consisted of
two pairs of decussate bracts and one ovule developed at
the axil of each of the lower fertile bracts (Fig.5d). Generally,
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the apices of the cones were flat, but in a few cones the
apices continued to develop to form a central columella
(Fig.5e). In one cone, the apices developed into an ovule
(Fig.5f). In addition, an abnormal cone with a bract initiated at the position corresponding to an ovule (Fig.5g).
The J. recurva var. coxii female cone had only one ovule
on the top of the cone axis, it was the simplest cone structure observed in all of the species studied. The bracts were
either decussate (Fig.5h) or in a whorl of three (Fig. 5i).
Fig.5. Scanning electron microscopy (SEM) photographs of dissected female cones of Juniperus chinensis (a－c), Juniperus
gaussenii (d－g) and Juniperus recurva var. coxii (h and i). a. The broad meristematic band (arrow) formed in the axil of the bract. b.
Ovule primordia initiated. c. A typical female cone of J. chinensis. d. A typical female cone of J. gaussenii. e. A cone apex developed
into a column. f. An ovule developed at the cone apex. g. An abnormal cone with a bract (star) initiated at the position corresponding
to an ovule. h, i. The female cone of J. recurva var. coxii has only one ovule terminal on the cone axis. Bar = 100 µm. Abbreviations:
B, removed bract; O, ovule; OP, ovule primordia.
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Fig.6. Diagrammatic transverse section through the middle of
bract scales, indicating three types of vascular system in the
female cones of the Cupressaceae. Arrows point to adaxial side.
Circles indicate the vascular bundles. The black half is xylem and
the white half is phloem. Dotted lines divide the vascular bundles
into three series that are derived from three traces (a central trace
and two lateral traces) at the base of the bract scale.
3 Discussion
In the systematics of the Cupressaceae, Cupressus and
Chamaecyparis have often been placed in the Cupresseae,
and Fokienia has also been placed in this tribe (Li, 1953;
Delectis Florae Reipublicae Popularis Sinicae Agendae
Academiae Sinicae Edita, 1978; Gadek et al., 2000). Our
demonstration of a strong similarity in the female cone
development of the Cupressus and Chamaecyparis genera is consistent with previous studies. Because the ovules
of Fokienia cones initiate in a distinct acropetal manner, it
may be appropriate to remove Fokienia from the
Cupresseae tribe.
One evolutionary trend in the female cones of the
Cupressaceae was constituted by a reduction in the number of ovules and bracts (Li, 1953). In the report of a study
on seed cones of fossil and extant Cupressaceae and
Taxodiaceae, Ohsawa (1994) proposed that the ancestral
seed cone of the Cupressaceae had an elongated form with
many bract-scale complexes. Later, reduction of the cone
axis probably took place to form a small spherical cone,
consisting of a small number of bract-scale complexes. We
previously found that ovule primordia of Thuja
occidentalis abort regularly (Zhang et al., 2001). Abortion
of ovules was also observed in Ch. lawsoniana, indicating that cones of its ancestor may have contained more
ovules. Cupressus cones contain numerous ovules,
whereas Juniperus has the simplest cones in the
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Cupressaceae, with just one ovule on each cone in J.
recurva var. coxii. Most strikingly, although many ovules
(up to 28) initiated in young Fokienia cones, only four to
eight ovules succeeded in developing into mature seeds.
Taking the evolutionary trends of female cones into
account, Fokienia is probably a relatively primitive genus
in the Cupressaceae, Juniperus is advanced, and
Cupressus and Chamaecyparis fall between Fokienia and
Juniperus.
It is now generally accepted that conifer seed cones
are compound structures in which the seed scale represents a modified branch borne in the axil of a bract scale. In
female cones of the Cupressaceae, the ovuliferous scale
and bract scale are completely fused (Owens and Molder,
1980; Gifford and Foster, 1989). The present study of the
ontogeny of female cones of the Cupressaceae implied
that “conifer seed cones are compound structures”is acceptable in principle. In the axil of the fertile bract, ovules
initiate on a broad meristematic swelling that might represent the secondary branch system. However, the idea about
a congenital fusion of a bract with an ovuliferous scale
was misleading. Because many researchers have claimed
completely fusion of the bract scale and ovuliferous scale
mainly on the basis of the inverted vascular bundles in the
scale of mature Cupressaceae cones (Lemoine-Sebastian,
1972; Gifford and Foster, 1989). In our studies, we identified three types of vascular systems in the female cones of
mature Cupressaceae cones: (A) The Juniperus,
Cupressus, Chamaecyparis, Fokienia, and Callitris
(Takaso and Tomlinson, 1989) had globular cones with
peltate bract-scales, as well as radial branching of the
strands forming two series of vascular bundles, including
an adaxial series of strands with an inverted xylem orientation and an abaxial system consisting of normally oriented
bundles (Figs.2, 6a). (B) In Calocedrus (unpublished data),
Platycladus (Zhang et al., 2000), and Libocedrus
(Tomlinson and Takaso, 2002), a single series of inverted
vascular bundles was generated in the adaxial side of the
thick, flat bract scale (Fig.6b). (C) The flat bract scale of
Thuja occidentalis contains no inverted vascular bundle
(Zhang et al., 2001) (Fig.6c). The results presented here
indicate that the inverted vascular bundles are the result
of bract scale development after pollination in conjunction with the intercalary growth of the bract. It appears
that the arrangement of the vascular system in mature
cones is related to the morphologies of the cone and the
bract scale. As the seed cone maturing, the bract functions as a seed-protecting structure, similar to the seed
scale in the Pinaceae.
ZHANG Quan et al.: Female Cone Development in Fokienia, Cupressus, Chamaecyparis and Juniperus (Cupressaceae)
Acknowledgements: Many thanks are due to Mr. YUE
Zhong-Shu, Ms. XIAO Hua and Dr. ZHOU Qi-Xing
(Kunming Botanical Garden, Kunming, Yunnan) for their
assistance in collecting cone samples. We are indebted to
Mr. XIAO Yin-Hou (Institute of Botany, The Chinese Academy of Sciences) for his help with SEM facilities.
１０８１
Napp-Zinn K, Hu Y S. 1989. Anatomical studies on the bracts in
pinaceous female cones Ⅲ. Comparative study of (mostly
Chinese) representatives of all genera. Bot Jahrb Syst, 110:
461－477.
Ohsawa T. 1994. Anatomy and relationships of petrified seed
cones of the Cupressaceae, Taxodiaceae and Sciadopityaceae.
References:
Delectis Florae Reipublicae Popularis Sinicae Agendae Academiae
Sinicae Edita . 1978. Flora Reipublicae Popularis Sinicae.
Tomus 7. Beijing: Science Press. 313－398. (in Chinese)
Farjon A, Garcia S O. 2003. Cone and ovule development in
Cunninghamia and Taiwania (Cupressaceae sensu lato) and
its significance for conifer evolution. Am J Bot, 90: 8－16.
Florin R. 1954. The female reproductive organs of conifers and
taxads. Biol Rev, 29: 367－389.
Fu L G, Yu Y F, Farjon A. 1999. Cupressaceae. Wu Z Y, Raven
P H. Flora of China. Vol. 4. St. Louis: Missouri Botanical
Garden Press. 62－77.
Gadek P A, Alpers D L, Heslewood M M, Quinn C J. 2000.
J Plant Res, 107: 503－512.
Owens J N, Molder M. 1980. Sexual reproduction in western red
cedar (Thuja plicata). Can J Bot, 58: 1376－1393.
Page C N. 1990. Cupressaceae. Kubitzki K. The Families and
Genera of Vascular Plants. Vol. 1. Pterdophytes and
Gymnosperms. Berlin: Springer-Verlag. 302－316.
Schulz C, Jagel A, Stützel T. 2003. Cone morphology in Juniperus
in the light of cone evolution in Cupressaceae s.l. Flora, 198:
161－177.
Shi L, Wang F H. 1989. Development of the megasporangiate
shoot of Taxaceae. Cathaya, 1: 83－91.
Sporne K R. 1971. The Morphology of Gymnosperms. London:
Hutchinson. 144－147.
Relationships within Cupressaceae sensu lato: a combined
Takaso T, Tomlinson P B. 1989. Cone and ovule development in
morphological and molecular approach. Am J Bot, 87: 1044－
Callitris (Cupressaceae, Callitroideae). Bot Gaz, 150: 378－
1057.
390.
Gifford E M, Foster A S. 1989. Morphology and Evolution of
Tomlinson P B, Takaso T. 2002. Seed cone structure in conifers in
Vascular Plants. New York: Freeman WH and Company. 424－
relation to development and pollination: a biological approach.
432.
Can J Bot, 80: 1250－1273.
Hart J A, Price R A. 1990. The genera of Cupressaceae (including
Wang H Y, Hu Y X, Wang F H. 1995. On the structure of female
Taxodiaceae) in the southeastern United States. J Arnold Arbor,
reproductive organs of Taxaceae and its systematic position.
71: 275－322.
Bot Res, 7: 42－47.
Hu Y S, Napp-Zinn K, Winne D. 1989. Comparative anatomy of
Zhang Q, Hu Y-X, Lin J-X. 2000. Ovule and seed cone develop-
seed-scale of female cones of Pinaceae. Bot Jahrb Syst, 111:
ment in Platycladus orientalis (Cupressaceae). Acta Bot Sin ,
63－85.
42: 564－569.
Lemoine-Sebastian C. 1972. Étude comparative de la vascularisation
Zhang Q , Hu Y-X, Lin J-X. 2001. Female cone development in
e t d u co mp l ex e s émin a l c h e z l e s c u p r es s ac ée s .
Thuja occidentalis (Cupressaceae). Acta Phytotax Sin , 39:
Phytomorphology, 22: 246－260.
45－50. (in Chinese with English abstract)
Li H L. 1953. A reclassification of Libocedrus and Cupressaceae.
J Arnold Arbor, 34: 17－35.
Lin J-X, Hu Y-S . 2000. Atalas of Structure of Gymnosperms.
Beijing: Science Press. (in Chinese)
(Managing editor: WANG Wei)