Estuarine, Coastal and Shelf Science 58 (2003) 587–600
Phytoliths of common grasses in the
coastal environments of southeastern USA
Houyuan Lua,b, Kam-biu Liub,*
a
Institute of Geology and Geophysics, Chinese Academy of Sciences, P.O. Box 9825,
Beijing 100029, China
b
Department of Geography and Anthropology, Louisiana State University, Baton Rouge, LA 70803, USA
Received 28 October 2002; received in revised form 8 May 2003; accepted 8 May 2003
Abstract
Thirty-four grass species were collected for phytolith analysis from a variety of coastal environments in the southeastern USA
(Georgia, Florida, and Louisiana), including salt marshes, freshwater/brackish marshes, pine/oak forests, maritime hardwood
forests, and sand dunes. Phytoliths produced by these modern grasses include a large diversity of shapes and types. We propose
a preliminary relationship between modern coastal plant communities and their predominant phytolith contents. The dominant
grasses of coastal sand dunes, such as Uniola paniculata, produce primarily flat tower and two-horned tower phytoliths. Rondel/
saddle ellipsoid phytoliths are mainly produced by Spartina alterniflora, the most common plant in coastal salt marshes. Rondel and
spool/horned tower phytoliths are common in brackish marsh grasses. Plants from interdune meadow produce primarily dumbbell
phytoliths, as well as small cross and Cyperaceae-type phytoliths. These results provide a basis for the interpretation of fossil
phytolith assemblages and the reconstruction of coastal environmental changes.
Ó 2003 Elsevier Ltd. All rights reserved.
Keywords: phytoliths; silica bodies; grasses; microfossils; coastal environments; Quaternary; southeastern USA
1. Introduction
Phytoliths are microscopic silica bodies that precipitate in or between cells of living plant tissues. They
occur in many plant families (Pearsall, 2000; Piperno,
1988, 2001), but are especially abundant, diverse, and
distinctive in the grass family (Gramineae) (Blackman,
1971; Brown, 1984; Clifford & Watson, 1977; Grob,
1896; Piperno & Pearsall, 1998; Prat, 1936; Twiss, 2001).
Many taxa in Gramineae are characterized by phytoliths
with specific morphological characteristics, hence their
taxonomic significance. Phytoliths are released from
plant tissues when they are decayed, burned, or digested.
Released phytoliths thus become microfossils of the
plants that produce them.
* Corresponding author.
E-mail address: [email protected] (Kam-biu Liu).
0272-7714/03/$ - see front matter Ó 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/S0272-7714(03)00137-9
Phytolith morphology and taxonomy, as well as
the application of phytolith analysis to archaeological
and paleoenvironmental research, have been the subject
of many studies (Bowdery, Hart, Lentfer, & Wallis,
2001; Horrocks, Deng, Ogden, & Sutton, 2000; Kondo,
Childs, & Atkinson, 1994; Lu et al., 1996; Madella,
1997; Meunier & Colin, 2001; Mulholland & Rapp,
1992; Pearsall & Piperno, 1993; Piperno, 1988; Rosen,
1992; Rovner, 1988; Wang & Lu, 1993). However, until
recently very little attention had been paid to the use
of phytoliths in the study of coastal environmental
changes (Fearn, 1998; Horrocks et al., 2000). In this
study, we conducted a pioneer investigation of phytoliths in modern grasses growing in the coastal environments of southeastern USA (Georgia, Florida, and
Louisiana).
The coastal zones of the southeastern USA consist of
a variety of ecological habitats and vegetation types.
Chief among them are sand dunes and interdune
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meadows, maritime or upland forests, swamps, fresh
marshes, brackish marshes, and salt marshes (Bertness,
1999). These coastal environments pose special challenges to Quaternary paleoenvironmental reconstruction using conventional paleoecological techniques such
as pollen analysis (e.g. Clark, 1986; Clark, Overpeck,
Webb, & Patterson, 1986; Clark & Patterson, 1985;
Davis, 1992). One of the constraints in the application of
pollen analysis is that some key coastal environments,
particularly salt and fresh/brackish marshes and to some
extent sand dunes, are dominated by grasses, but, except
for Zeas mays (maize), Gramineae pollen cannot be
identified below the family level (Fearn & Liu, 1997).
Here we demonstrate that this constraint can be overcome by phytolith analysis, because characteristic grasses
of different coastal environments produce different
phytolith assemblages.
2. Phytolith classification
At present, the classification of phytoliths is principally based on the study of some modern Gramineae,
Xylophyta, and a few other plants. Different researchers
have suggested different terms and classification schemes
because of the differences in materials, classification
criteria, and study areas. So far, no uniform and
convenient classification scheme has been widely adopted for various conditions. Nevertheless, many important investigations have made a great contribution to
phytolith classification. Taking Gramineae phytoliths as
an example, Prat (1936) divided the Panicoideae subfamily into two groups by studying the shapes of short
cells in the leaf veins of some genera of Gramineae.
Twiss, Suess, and Smith (1969) classified Gramineae
phytoliths into four groups after they summarized the
achievements of Prat (1936) and other researchers.
Brown (1984) classified Gramineae phytoliths into eight
categories including more than 130 types after studying
the phytoliths from different parts of 112 taxa of
Gramineae plants. Piperno (1988) presented an index
table of two different kinds of phytoliths. Mulholland
and Rapp (1992) proposed one morphological classification of grass silica bodies after summarizing different
researchers’ classifications for the Gramineae family.
Piperno and Pearsall (1998) summarized the distribution
of short-cell phytoliths from the grasses, which were
described as circular to oval-(rondels), saddle-, bilobate-,
or cross-shaped, and well-established diagnostic features
of the leaf epidermis.
The above classification of phytoliths was mainly
proposed by European and American botanists. Japanese researchers such as Sase and Kondo (1974)
developed a morphological classification, which added
the following three classes: fan-shape, point-shape, and
bambusoid. Kondo et al. (1994) classified Gramineae
phytoliths into nine classes based on a modified classification of Kondo and Sase (1986). In China, Wang
and Lu (1993) classified grass phytoliths into 15 classes.
Table 1 attempts to compare and reconcile the main
classifications of grass phytoliths proposed by various
researchers.
The dumbbell (lobate) phytolith originates from the
epidermal cells (shortcells) of Panicoideae and Oryzoideae, some Arundinoideae, and Chloridoideae subfamilies (Brown, 1984; Fearn, 1998; Lu & Liu, 2003;
Mulholland, 1989). Table 1 shows that different researchers mostly subdivided the dumbbell into three
groups: 1, dumbbell or bilobate, lobate; 2, complex
dumbbell or multilobed, polylobates; and 3, cross.
The Chloridoid class (Twiss et al., 1969) consists of
only two types of saddle-shaped bodies; one is the
Chloridoid type (Table 1), which originates from
epidermal cells (short cells) of Chloridoideae, and some
Bambusoideae and Arundinoideae subfamilies. They
have the form of short saddles (short seat) with nonwrinkly surface, and have been described elsewhere as
Ôbattle-axes with a double edgeÕ (Kondo et al., 1994;
Prat, 1936). This type was referred to as the short saddle
type, short plateau saddle type, or Chloridoid class by
Wang and Lu (1993), Piperno and Pearsall (1998), and
Kondo et al. (1994), respectively. Another is the thin
Chloridoid type, which is saddle shaped, similar to
Chloridoid type, but longer. They may have a wrinkly
and/or a non-wrinkly surface. This type was called the
long saddle type, tall collapsed saddle type, or Bambusid
class by Wang and Lu (1993), Piperno and Pearsall
(1998), and Kondo et al. (1994), respectively.
Pearsall (1989) and Pearsall and Trimble (1983, 1984)
found six commonly occurring phytolith types, then
referred to as horned towers, flat towers regular spools,
irregular spool, angular, and half rotated. Kondo et al.
(1994) developed both Chionochloid class and Ôphytoliths from other short-cellsÕ class based on these shapes.
It is difficult to relate these types to grass taxonomy and
to infer moisture and temperature conditions from their
occurrence (Pearsall, 1989, 2000).
The Festucoid class (Twiss et al., 1969) contains
several geometrical types that are circular, rectangular,
elliptical, or oblong. Kondo et al. (1994) and Pearsall
(1989) used the same term of Festucoid class to define
the short-cell phytolith types as originating from the
epidermal cells of the Pooideae subfamily. They also
used different geometrical terms—boat-shape, hatshape, rectangular, and round/oblong—to describe
Twiss’ (1969) circular, rectangular, elliptical, and oblong
types. Current groupings within the Festucoid class
include two major geometrical types. One is trapezoids
(Brown, 1984), which correspond to wavy trapezoid
(Piperno & Pearsall, 1998), rectangular (Mulholland &
Rapp, 1992; Pearsall, 1989), boat-shaped (Kondo et al.,
Table 1
Comparison of different grass phytolith classification systems
Lu et al., 1996 and
Wang and Lu, 1993
Piperno and
Pearsall, 1998
(short cell)
Dumbbell
Brown, 1984
Bilobate
Panicoid class
(dumbbell)
VI Bilobates
Multilobed short cell
(Complex dumbbell)
VII Polylobates?
Cross
(Cross)
VIII Crosses
Tall saddle/long saddle
Chioridoid class
(thin Chloridoid)
IV Saddles
Sase and
Kondo,
1974
Kondo et al.,
1994
Mulholland and
Rapp, 1992
(short cell)
Panicoid shapes
(dumbbell, angular,
nodular, cross,
crenate,
half dumbbell)
Panicoid
Panicoid class
Dumbbell
(Complex regular
bilobate?)
Cross
Chloridoid shapes
(saddles)
Chloridoid
Bambusid class
Collapsed saddle
Saddle: one
concave edge
Saddle: no
concave edges
Narrow-elliptate
Short saddle
Multiple tooth
Weakly tooth
Hat
Fan type with
raised ridge
Fan type without
raised ridge
Square
Rectangle
Plate-like bar
Point (joint) bar
Smooth-bar
Long-point
Short-point
Short saddle
Plateau saddle
Conical?
Bilobate/saddle conical
irregular short cell
Wavy trapezoid
Saddle: two
concave edges
(Chloridoid)
Festucoid class
(circular rectangular
elliptical oblong)
Rondel
(circular to oval)
Elongate class
Chloridoid class
V Trapezoids
Horned towers,
flat towers, regular spools
Half rotated, angular,
irregular spool
Festucoid shapes
(square/rectangular)
Pooid
(Festuoid)
Chionochloid class
Triangle?
Phytolith from
other short cell
Festucoid class
(boat-shaped)
Pentagon?
III Double outlines
(Round/oblong)
(Hat/cone-shaped)
I Plates (IB)
Bulliform cells
Fan-shaped
Fan-shaped class
I Plates (IA)
Long cells
Elongate
Elongate class
II Trichomes
Trichomes
Point-shaped
Point-shaped class
Sinuate:
polyloate
bilobate?
Rectangle
Rondel (entire,
flat, indented)
H. Lu, K.B. Liu / Estuarine, Coastal and Shelf Science 58 (2003) 587–600
Long saddle
Twiss et al., 1969
Pearsall, 1989 and
Pearsall and
Trimble, 1983
589
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1994), and tooth-shaped (Wang & Lu, 1993). Another is
double outlines (Brown, 1984), which correspond to
rondel (Mulholland & Rapp, 1992; Pearsall, 1989;
Piperno & Pearsall, 1998) and hat/cone-shaped phytoliths (Kondo et al., 1994; Wang & Lu, 1993).
Biogenic silica can also deposit in bulliform (motor)
cells, prickle hairs (Trichomes), long cells, stomata, and
vascular tissues of grass epidermis. They can also form
in subepidermal cells, forming easily recognizable
bodies. The phytolith shapes from bulliform cells,
prickle hairs, long cells, and non-short cells of leaves
have been described as fan, elongate, point, square, and
plates by Twiss et al. (1969), Kondo et al. (1994), Wang
and Lu (1993), and Brown (1984). These forms do not
possess any subfamily or tribal characteristics, but have
secondary features allowing further subdivision (Wang
& Lu, 1993).
As for non-Gramineae plants, Kondo and Pearson
(1981) and Kondo and Sumda (1978) classified phytoliths of gymnosperm and monocotyledonous angiosperm trees into six groups, and those of dicotyledonous
angiosperm trees into eight groups based on studies of
a wide range of native and exotic trees in Japan. A great
diversity of phytoliths shapes from dicotyledon species
has been described by Bozarth (1992), Geis (1973),
Piperno (1988), and Runge (1999). Ollendorf (1992)
proposed a classification scheme for sedge (Cyperaceae)
phytoliths.
While all these various classification systems have
advanced the young science of phytolith study, significant shortcomings and discrepancies remain. Some
classification systems are only suitable for detailed study
of modern plants. Some other classification schemes are
only applicable to regional floras.
Phytoliths produced in grass epidermis can be divided
into two broad morphological classes—bodies in long
cells and bodies in short cells (Metcalf, 1960). Long-cell
silica bodies are variable in shape but tend to be
elongate with sinuous, often interlocking borders. But
like their bulliform or prickle hair counterparts, the
elongate phytoliths also do not posses any subfamily or
tribal characteristics. By contrast, short-cell phytoliths
can be generally classified into distinctive grass subfamilies (Piperno & Pearsall, 1998; Twiss et al., 1969).
Although the previously published grass short-cell
phytolith classification schemes have much in common,
significant differences in terminology and in emphasis on
specific morphological characteristics remain. In this
study, we use a descriptive name to describe each
morpho-type. Each short-cell phytolith has been classified into one of 11 basic morpho-types based on Pearsall
(1989), Piperno and Pearsall (1998), and this study. The
11 morpho-types are dumbbell, cross, long saddle, short
saddle, plateau saddle, rondel, flat tower, two-horned
tower, spool/horned tower, rondel/saddle ellipsoid, and
wavy trapezoid (Fig. 1).
3. Materials and methods
3.1. Samples of modern plants for analysis
of phytoliths
Sixty species of modern plants (including 34 species
of grasses) were collected for phytolith analysis from the
Atlantic and Gulf of Mexico coasts of the southeastern
USA in the summers of 1999 and 2000. The principal
sampling sites are Cumberland Island in southern
Georgia and the Gulf coastal regions of northwestern
Florida and Louisiana. The samples were collected from
a variety of coastal or near-coastal environments, such as
salt marshes, pine/oak forests, maritime hardwood forests,
freshwater and brackish marshes, and sand dunes (Table
2). Each plant sample includes leaves, culms, inflorescences, and roots. Twenty-five grass genera representing all
six subfamilies (Pooideae, Panicoideae, Chloridoideae,
Bambusoideae, Oryzoideae, and Arundinoideae, see
Gould & Shaw, 1983) were included in the samples.
Twenty-five of the 34 grass species included in this
study belong to two subfamilies, Panicoideae and
Chloridoideae. Grasses in Panicoideae are distributed
widely in humid tropical or subtropical areas (Gould &
Shaw, 1983). The most suitable growing condition for
grasses of this subfamily is in the southeastern USA,
while the poorest is in the northwest (Gould & Shaw,
1983). Although temperature is a primary limiting
factor, a few species are adapted to dry conditions,
and moisture supply becomes an important secondary
limiting factor. The Chloridoideae is widely distributed
over the North American continent, but its frequency is
highest in the southwestern USA and northern Mexico
(Gould & Shaw, 1983). There, under a warm and dry
climate, over 50% of the grass species are Chloridoid.
Although in this study we have not collected all the grass
species occurring in the coastal flora, we focused on the
typical or common grasses of the key coastal environments in the southeastern USA. For example, our
samples include Uniola paniculata and Aristida desmantha of the sand dunes, Spartina alterniflora of the salt
marshes, Spartina patens of the brackish marshes,
Arundinaria longifolia of the maritime forest edges, and
Phragmites australis of the fresh marshes (Bertness,
1999; Gosselink, 1984; Wiegert & Freeman, 1990).
3.2. Methods of extracting phytoliths
from modern plants
All the collected plant samples were cleaned with
distilled water in an ultrasonic water bath to remove
adhering particles. Leaves and culms of each species
were placed in 20 ml of saturated nitric acid for one
night to oxidize organic materials completely. The
solutions were centrifuged at 2000 rpm for 10 min,
H. Lu, K.B. Liu / Estuarine, Coastal and Shelf Science 58 (2003) 587–600
591
Fig. 1. Hand drawings of principal morpho-types of short-cell phytoliths found in the 34 species of coastal grasses from the southeastern USA.
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H. Lu, K.B. Liu / Estuarine, Coastal and Shelf Science 58 (2003) 587–600
Table 2
List of 34 modern grasses from the US Atlantic and Gulf coasts used for the phytolith analysisa
No.
Name
Subfamily (Gould
& Shaw, 1983)
Ecology or distribution of plants (Allen, 1992; Gould &
Shaw, 1983)
1
2
3
4
5
6
7
8
9
10
11
12
13
Andropogon glomeratus (Walt.) BSP
Andropogon ternaries Michx.
Anthaenatia rufa (Nutt.) Schult.
Aristida desmantha Trin. and Rupr.
Arundinaria longifolia E. Fourn
Arundinaria gigantea (Walt.) Muhl.
Avena sativa L.
Cenchrus incertus M. Curtis
Chasmanthium laxum (L.) Yates.
Chasmanthium ornithorhynchum (Steud.) Yates
Ctenium aromaticum (Walter) A.W. Wood
Dactyloctenium aegyptium (L.) Willd.
Distichlis spicata (L.) Greene
Panicoideae
Panicoideae
Panicoideae
Chloridoideae
Bambusoideae
Bambusoideae
Pooideae
Panicoideae
Arundinoideae
Arundinoideae
Chloridoideae
Chloridoideae
Chloridoideae
14
15
16
17
18
Eragrostis oxylepis (Torr.) Torr.
Eragrostis cilianensis (All.) Vignolo-Lutati
Erianthus strictus Spreng.
Eustachys petraea (Sw.) Desv.
Leersia oryzoides (L.) Sw.
Chloridoideae
Chloridoideae
Panicoideae
Chloridoideae
Oryzoideae
19
20
Panicum amarum Elliott
Panicum dichotomiforom Michx.
Panicoideae
Panicoideae
21
Panicum hemitomon Schult.
Panicoideae
22
Panicum verrucosum Muhl.
Panicoideae
23
Panicum virgatum L.
Panicoideae
24
25
26
27
28
Phragmites australis (Cav.) Trin. Ex Steud.
Poa annua L.
Saccharum officinarum L.
Setaria sp.
Sorgastrum nutans (L.) Nash
Arundinoideae
Pooideae
Panicoideae
Panicoideae
Panicoideae
29
30
31
32
33
34
Sorghum halepense (L.) Pers.
Spartina alterniflora Loisel
Spartina patens (Ait.) Muhl.
Sporobolus virginicus (L.) Kunth.
Uniola paniculata L.
Zizaniopsis miliacea (Michx.) Doell and Aschers.
Panicoideae
Chloridoideae
Chloridoideae
Chloridoideae
Chloridoideae
Oryzoideae
Generally on wet sites
Edge of pine forest
Pine forest
Sandy soil along coast
Edge of forest
Pine forest or edge of flatwoods
Disturbed areas
Dry sand
Edge of forest
Moist area
Edge of forest, interdune meadow
Southeast and west USA
Saline areas in coastal marshes and
islands, sandy beaches
Sandy soil along the coast
Sandy soil along the coast
Edge of pine forest and disturbed areas
Sandy soil along the coast
Wet roadside ditches and edges of lakes,
streams, and other wet areas
Sandy soil along coast, interdune meadow
Disturbed areas, especially in moist
regions, throughout USA
Coastal marshes, wet areas and in the
inland part of coastal sites, interdune meadow
Disturbed areas and edges of forests,
mostly in pine regions
Edges of pine forests and remnant strips
in prairie regions; cheniers and spoil
banks in coastal freshwater marshes
Fresh to brackish water marshes
Disturbed areas throughout USA
Cultivated in tropical regions of the world
?
Edge of forest and disturbed areas in pine and
prairie regions
Widespread throughout the world
Salt marshes and sandy areas on coast
Brackish to saline areas in coastal marshes
Sandy soil along the coast
Sandy soil along the coast
Edges of lakes, streams, wet roadside ditches
a
All plant samples are preserved in the Department of Geography and Anthropology, Louisiana State University, Baton Rouge, LA 70803, USA.
decanted, and rinsed twice with distilled water. They
were then rinsed with 95% ethanol until the supernatant
was clear. The phytolith sediments were transferred to
storage vials. The residual subsamples were mounted
onto microscopic slides in Canada Balsam medium for
photomicrography and in liquid (glycerol) medium for
counting and line drawing. A minimum of 350 phytolith
grains were counted in each sample.
Light photomicrography at 400 magnification was
used to record typical types of phytoliths found in plant
tissues. A multitude of phytolith types were isolated
from the grass samples analyzed. A few of them have
not been reported previously in the phytolith literature.
4. Results and discussion
4.1. Distribution of short-cell phytolith types
observed in coastal grasses
Eleven morpho-types of short-cell phytoliths were
found among the 34 grass species included in this study
(Fig. 1 and Table 3). The different morpho-types of
selected common coastal grasses are illustrated or
photomicrographed in Plates 1–3. Our photomicrographic and hand-drawn illustrative key herein is
designed to aid the identification of phytoliths commonly found in Quaternary or archaeological deposits.
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H. Lu, K.B. Liu / Estuarine, Coastal and Shelf Science 58 (2003) 587–600
being the most characteristic markers of the Panicoideae
(Twiss et al., 1969), dumbbell and cross phytoliths are
also found to be present in the Chloridoideae (Aristida
desmantha and Ctenium aromaticum) and Arundinoideae (Chasmanthium laxum and Chasmanthium ornithorhynchum) subfamilies in this study (Table 3).
The term ÔdumbbellÕ was first used by Metcalf (1960)
as a morphological term for the shape of some intercostal short-cell phytoliths. It has gradually become a
name given to a loosely defined group of phytoliths
characterized by having two lobes joined by a shank.
However, many subsequent researchers, including Brown
Lobate phytoliths, including the dumbbell and cross
types according to the traditional nomenclature, have
been identified consistently as distinctive silica bodies
(Lu & Liu, 2003). Dumbbells are characterized by
having two somewhat rounded lobes connected by
a shaft. Some (complex types) have one or two additional lobes on the shaft. Crosses are shorter, nearly
equidimensional bodies with four distinct lobes. All
specimens of plants from Panicoideae (Fig. 1 and Plate
1A, D) and Oryzoideae (Plate 1B) grasses in this study
have typical dumbbell type. The crosses are mostly
associated with the Panicoideae subfamily. Despite
Table 3
Distribution of short cell phytolith types observed in coastal grasses
Taxon
Long Short Plateau
Flat Two-horned Spool/horned Rondel/saddle Wavy
Dumbbell Cross saddle saddle saddle Rondel tower tower
tower
ellipsoid
trapezoid
Panicoideae
Andropogon glomeratus
Andropogon ternaries
Anthaenatia rufa
Cenchrus incertus
Erianthus strictus
Panicum amarum
Panicum dichotomiflorum
Panicum hemitomon
Panicum verrucosum
Panicum virgatum
Saccharum officinarum
Setaria sp.
Sorgastrum nutans
Sorghum halepense
A*
A*
A*
A*
A*
A*
A*
A*
A*
A*
A*
A*
A*
A*
Chloridoideae
Aristida desmantha
Ctenium aromaticum
Dactyloctenium
aegyptium
Distichlis spicata
Eragrostis oxylepis
Eragrostis cilianensis
Eustachys petraea
Spartina alterniflora
Spartina patens
Sporobolus virginicus
Uniola paniculate
C
C*
R*
R
C*
C*
R
R
C
R
C
R*
A*
C
R?
A?
A
C
A*
R
A*
A*
A*
R*
R
C
R
Bambusoideae
Arundinaria longifolia
Arundinaria gigantean
A*
A*
Oryzoideae
Leersia oryzoides
Zizaniopsis miliacea
R*
C*
A
A
R
R
R
R
R
A
C
R
C
A
A
C
R
R
R
A
R
A*
A*
R
R
R
A*
C
A
C
R
R
A
A
C
R
R
C
R
R
R
R
R
Pooideae
Avena sativa
Poa annua
Arundinoideae
Chasmanthium laxum
Chasmanthium
ornithorhynchum
Phragmites australis
C
R
C
C
R
C
A, abundant; C, common; R, rare; * diagnostic forms present, characteristic of taxon’s subfamily.
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H. Lu, K.B. Liu / Estuarine, Coastal and Shelf Science 58 (2003) 587–600
Plate 1. Illustrations of long-cell and short-cell phytolith morpho-types in four common coastal grass species: A, Panicum verrucosum (mostly
dumbbells); B, Leersia oryzoides (mostly dumbbells, some flat towers); C, Aristida desmantha (mostly tower-shaped phytoliths, some dumbbells);
D, Panicum hemitomon (mostly dumbbells). One scale ¼ 10 lm.
(1984), Fredlund and Tieszen (1994, 1997), and Piperno
and Pearsall (1998) have avoided using this term and
favored the alternative term ÔbilobateÕ. Recently Lu and
Liu (2003) documented the variability of 25 diagnostic
dumbbell (lobate) phytolith shapes occurring among 85
modern grass species collected from a variety of environments in China and the southeastern USA.
The short saddle morpho-type is produced in a high
proportion by the Chloridoideae. The descriptive term,
Ôbattle-axes with double edgesÕ (Prat, 1936), refers to the
outline of the base when the body is oriented in top
view. Saddle-shaped phytoliths are the dominant class of
the Chloridoideae subfamily (Fig. 1 and Plate 3C). They
are also common in two species of the Bambusoideae
H. Lu, K.B. Liu / Estuarine, Coastal and Shelf Science 58 (2003) 587–600
595
Plate 2. Illustrations and photomicrographs of different phytolith morpho-types in three common coastal grass species: A, Spartina alterniflora
(mostly rondel/saddle ellipsoid phytoliths); B, Uniola paniculata (mostly flat towers, some two-horned towers and spool/horned towers); and C,
Spartina patens (mostly spool/horned towers).
(Arundinaria longifolia, Arundinaria gigantea), and are
present in Phragmites australis (Arundinoideae) as well
(Table 3).
A great quantity of Ôrondel/saddle ellipsoidÕ morphotypes are isolated from Spartina alterniflora (Chloridoideae) (Fig. 1 and Plate 2A), with both round and saddle
tendencies. Spartina alterniflora (cordgrass) is a tall,
stiff-stemmed grass typically growing in salt marshes.
On the other hand, the spool/horned tower type (Fig. 1
and Plate 2C) is produced primarily in brackish marsh
grasses, such as Spartina patens (salt-meadow hay) and
Distichlis spicata. This type is equal to the Chionochloid
class of Kondo et al. (1994) and the regular spools of
Pearsall (1989).
A great number of phytoliths called Ôplateau saddlesÕ
are isolated from the leaves of Phragmites (Plate 3D).
More study is needed before they can be assigned genusspecific status, but they can be used as a marker of the
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H. Lu, K.B. Liu / Estuarine, Coastal and Shelf Science 58 (2003) 587–600
Plate 3. Photomicrographs of principal phytolith morpho-types in four common coastal grass species: A, Arundinaria longifolia (mostly long
saddles); B, Avena sativa (mostly wavy trapezoid); C, Dactyloctenium aegyptium (mostly short saddles); and D, Phragmites australis (mostly plateau
saddles) (bar unit in this plate is lm).
H. Lu, K.B. Liu / Estuarine, Coastal and Shelf Science 58 (2003) 587–600
Arundinoideae and to determine the possible presence
of Phragmites in soil phytolith assemblages. Kondo and
Sase (1986) distinguished the saddle from Phragmites as
Ômiddle saddleÕ, which is shorter than the Ôlong saddleÕ
from Bambusoideae and longer than the Ôshort saddleÕ
from Chloridoideae.
Bambusoideae contributes a large number of diagnostic types at the family level, particularly the long
saddle phytoliths with a wrinkly and/or non-wrinkly
surface (Plate 3A). The length of saddle from Bambusoideae is longer than that from Chloridoideae.
Rondels (circular to oval phytoliths) and wavy
trapezoids (Mulholland, 1989) are most closely associated with Pooideae. Wavy trapezoid (Plate 3B), in
particular, appears to be unique to Pooideae. The
rondels are also found in the Chloridoideae (Table 3).
Some types of phytoliths from coastal grasses do not
lend themselves to easy description. For example, flat
towers, two-horned towers, and spool/horned towers
(Fig. 1 and Plate 2B, C) are typically small, irregular
phytoliths. Although some researchers avoided using
these descriptive terms (flat towers, two-horned towers,
and spool/horned towers), no uniform or standard
terminology has been adopted in the literature. These
phytoliths warrant further investigation, as some of
them are likely to be of precise taxonomic value. They
have been isolated in great numbers from the Chloridoideae. In particular, flat towers are produced in high
proportions (>90%) by Uniola paniculata (sea oats)
(Plate 2B), a C4 grass typically occurring in primary
dunes or other sandy substrates along the coast.
The sinuate elongate, smooth elongate, point, fanshaped, square, and rectangle morpho-types (Plate 1A,
D) are derived from epidermic long cells, trichome cells,
and bulliform cells of grasses. They have no taxonomic
significance in our classification.
Non-Gramineae families from coastal environments
can also produce typical phytolith morpho-types. For
example, the cone-shaped morpho-type is attributed to
the Cyperaceae (sedge) family, and the circular crenate
to Sabal minor (saw palmetto).
Even though this study has not described all the short
cell phytoliths occurring in the coastal flora, our samples
include grasses that are common or diagnostic of most
of the ecologically important coastal environments in
the southeastern USA. More studies are needed that
would include additional species in the larger genera of
the Gramineae, as well as in other non-Gramineae taxa.
4.2. Typical assemblages of grass phytoliths
in coastal environments
Grasses occur in nearly all habitats throughout the
coastal environments of the southeastern USA (Bertness, 1999; Gosselink, 1984; Wiegert & Freeman, 1990).
Vegetation in the coastal zone is strongly affected by
597
various environmental gradients. Perhaps the most
important factors are topography and salinity. Some
of the drier habitats on the coast include beach ridges
and sand dunes, where Uniola paniculata (sea oats),
Sporobolus virginicus (marshgrass, crabgrass), Aristida
desmantha (curly threeawn), Distichlis spicata (saltgrass), and Eragrostis cilianensis (stinkgrass) occur.
The coastal marsh is characterized by large populations
of relatively few species. Spartina alterniflora (cordgrass)
is the dominant plant in salt marshes. Brackish marshes,
developed extensively in estuaries and deltas, and on the
peripheries of bays and lagoons, are often dominated by
Spartina patens (salt-meadow hay). Other common grass
species in brackish marshes include D. spicata, Leersia
oryzoides, and Panicum hemitomon. Fresh marshes are
dominated by Panicum virgatum, P. hemitomon, and
Phragmites australis. Swamps occupy the area between
upland forests and coastal marshes. In these wetland
forests common trees include Taxodium distichum, Salix
nigra, Sabal minor, Nyssa aquatica, and Quercus spp.
Some grass species commonly found in the swamps are
Panicum spp., Eragrostis spp., and Zizaniopsis miliacea.
Phytolith analysis of the grasses from different
coastal vegetation communities shows significant variation in shapes and assemblages (Fig. 2). Rondel/saddle
ellipsoid phytoliths are mainly produced by Spartina
alterniflora, the most common plant in the salt marshes.
Thus the predominance of rondel/saddle ellipsoid
phytoliths in a sediment sample may be a good indicator
of salt marsh environment. Rondel and spool/horned
tower phytoliths are common in grasses from brackish
marshes, such as Spartina patens. Flat towers, twohorned towers, and short saddle-shaped phytoliths
dominate the grass samples from sand dunes, especially
Uniola paniculata. Plateau saddle and dumbbell phytoliths are common in the grass samples from fresh
marshes, such as Phragmites australis. The grass samples
from coastal swamps produce many dumbbell phytoliths. The long saddle phytoliths are exclusively derived
from Bambusoideae such as Arundinaria spp., which
commonly occurs on the edge of upland forests or
maritime forests. They are distinctly larger than the
plateau saddle phytoliths typically found in Phragmites.
Trees from maritime forests also produce typical
phytolith shapes such as the circular crenate type from
palms (Pearsall, 1989, 2000), and tracheid, polyhedron
shape from other broad-leaved hardwood trees (Kondo
et al., 1994).
Although our study is based on the phytolith
contents of grass plants, the conclusions are supported
by the results of phytolith analysis of soil samples
collected from the corresponding coastal environments.
In the 50 surface soil samples collected for phytolith
analysis from different environments along the Atlantic
and Gulf coasts of the southeastern USA (Lu & Liu,
2001), we found that the modern phytolith composition
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H. Lu, K.B. Liu / Estuarine, Coastal and Shelf Science 58 (2003) 587–600
Fig. 2. An idealized transect of coastal environments in the southeastern USA showing major vegetation zones and their representative phytolith
assemblages. The width of a black bar indicates relative abundance of each phytolith type.
in the primary dunes is well characterized by a high
amount of two-horned towers (30 25%), flat towers
(13 7%), and short saddle (9 6%) phytoliths. The
phytolith composition from the surface samples in
interdune meadow shows very high values of dumbbell
phytoliths (47 13%). Both the Palmae (circular crenate)
morpho-types and other broad-leaved types account for
more than 60–80% of all phytoliths, and grass phytoliths
account for less than 20% in the modern soils under
maritime forests (Lu & Liu, 2001).
Our study demonstrates the high potential of
phytolith analysis as a tool for identifying vegetation
in coastal environments. Each of the key coastal environments yielded abundant and distinctive phytolith
assemblages.
5. Conclusions
Phytolith analysis of modern grasses from various
coastal environments including salt marshes, brackish
marshes, freshwater marshes, pine/oak forests, maritime
hardwood forests, and sand dunes in the southeastern
USA has revealed a large diversity of phytolith shapes.
The dominant grasses from coastal sand dunes, such as
Uniola paniculata, and Eragrostis spp., produce primarily flat towers and two-horned towers, as well as small
short saddle and dumbbell-shaped phytoliths. The
grasses and sedges from interdune meadows, such as
Panicum spp., Cenchrus incertus, and Cyperaceae, produce primarily dumbbell, small cross, and Cyperaceae
phytoliths. The Pooideae and Bambusoideae subfamilies
of grasses, which are generally common along the edges
or on the understory of maritime forests, produce wavy
trapezoid and long saddle phytolith, respectively. The
dominant grasses of swamps produce primarily dumbbell and plateau saddle phytoliths. Rondel/saddle
ellipsoid phytoliths are almost exclusively produced by
Spartina alterniflora, the dominant plant in salt marshes.
Thus the predominance of rondel/saddle ellipsoid
phytoliths in a sediment sample may be a good indicator
of salt marsh environment. Rondel and spool/horned
tower phytolith are common in grasses from brackish
marshes.
This study provides a basis for the interpretation of
fossil grass phytolith assemblages recovered from
coastal sediments for the reconstruction of coastal
environmental changes. Some coastal environments,
such as salt marshes and brackish marshes, may not be
easily distinguishable based on their pollen assemblages
H. Lu, K.B. Liu / Estuarine, Coastal and Shelf Science 58 (2003) 587–600
(e.g. see Chmura, 1994; Clark, 1986; Clark & Patterson,
1985; Fearn, 1998). Other environments, such as sand
dunes, are palynologically unidentifiable because pollen
is absent or rare due to poor preservation. Our
investigation demonstrates that these key coastal
environments (salt marshes, brackish marshes, and sand
dunes) produce distinctive phytolith assemblages that
can be used as a supplementary tool in coastal
paleoenvironmental reconstructions (Lu & Liu, 2001).
Acknowledgements
We thank X.Y. Zhou and Carl A. Reese for
providing modern grass reference samples and for
helpful discussion. This work was supported by grants
from Risk Prediction Initiative (RPI) of the Bermuda
Biological Station for Research (RPI-00-1–002), and by
the US National Science Foundation (SES-8922033,
SES-9122058, and BCS-0213884), and NSFC (40024202,
40271117).
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