ANTHOPHYTA
17. GRAMINEAE (POACEAE)
Annual or perennial herbs, rarely woody and shrub- or vinelike (bamboos), sometimes aquatic, rarely armed (Guadua); stems terete, often arising from stolons or rhizomes. Leaves alternate, 2-ranked, petiolate; petioles sheathing, ligulate; blades simple, entire; venation paral- lel. Flowers bisexual or unisexual (monoecious or in Gynerium dioecious), more or less zygomorphic, in usu- ally terminal panicles, racemes, or spikes; flowers com- pounded in the highly modified spikelets consisting generally of 2 bracts, the glumes subtending a rachilla, the rachilla bearing 1 to many sessile flowers, each flower generally subtended by usually 2 bracts, the lemma, and the palea; perianth reduced to 2 or sometimes 3 inconspic- uous lodicules; stamens 3 or sometimes 6, free; anthers 2-celled, dehiscing longitudinally; ovary 1, 1-locular, 3-carpellate; ovule 1, usually anatropous; styles 2 or rarely 3, simple; stigmas generally plumose. Fruit a caryopsis (in Sporoholus the pericarp free from the seed and sub- achenial); seeds having starchy endosperm.
Flowers are principally wind pollinated (Faegri & van der Pijl, 1966), though some forest grasses such as Olyra and Lithachne are visited and perhaps pollinated by insects (Soderstrom & Calderon, 1971). Both of these genera are monoecious and have plumose stigmas. It is believed that the pistillate flowers may receive pollen accidentally from insects that visit the staminate flowers
KEY TO THE TAXA OF GRAMINEAE
Plants bamboolike or at least with one, often woody main culm (Chusguea only slightly woody), the branches much smaller than the main culm, often fasciculate or whorled at nodes:
Main culms more than 1 cm wide, often armed; cultivated at the Laboratory Clearing or rare in the forest Bambusa Main culms less than 1 cm wide, usually much less, unarmed; common in the forest and along
the shore:
Blades lacking a prominent tuft of trichomes near the base on lower surface (puberulent throughout below and with longer but not tufted trichomes near base); all veins ± equal;
plants usually growing in dense clumps Rkipidocladum racemiflorum (Steud.) McClure Blades densely tufted near the base on lower surface (otherwise only minutely scabridulous);
midrib more prominent than other veins; plants growing in small clumps or solitary Chusguea simpliciflora Munro Plants herbaceous (woody with subglobose spikelets in Lasiacis), the branches when present not
much smaller than the main culm:
Inflorescence a solitary spike or a solitary spikelike raceme or panicle:
Inflorescence with conspicuous, threadlike bristles or awns (longer than the spikelet proper):
Spikelets subtended by straight bristles (more than 1 per spikelet except sometimes in Se- taria vulpiseta):
Inflorescence a true spike; spikelets sessile, enclosed in burs subtended by a ring of re- trorsely barbed bristles Cenchms brownii R. & S.
Inflorescence a spikelike panicle; spikelets subtended by a few, antrorsely barbed bristles Setaria Spikelets lacking bristles:
Awns less than 2 cm long, geniculate, then straight to the apex; plants of clearings:
Racemes to 5.5 cm long; spikelets lacking transverse ridges, pubescent throughout;
awns less than 8 mm long Polytrias amaura (Miq.) O. Kuntze Racemes usually more than 6 cm long; spikelets with prominent transverse ridges,
densely pubescent only near base; awns ca 15 mm long ... Ischaemum rugosum Salisb.
Awns 2 cm or more long, often prominently curled at apex; plants growing only within the forest:
Blades linear, more than 30 cm long, usually less than 2.2 cm wide Streptogyne americana C. E. Hubb.
Blades mostly narrowly lanceolate-elliptic, less than 30 cm long, more than 2.5 cm wide Streptochaeta Inflorescence lacking conspicuous, threadlike awns or bristles (the spikelet sometimes nar-
rowed to a point but this seldom as long as the spikelet proper):
Inflorescences less than 3.5 cm long; spikelets obovate, in pairs; plants creeping, often small; growing in clearings Paspalum decumbens Sw.
Inflorescences more than 5 cm long; spikelets not obovate; plants erect:
Inflorescence a spikelike panicle, the branches slender, bearing several pedicellate spike- lets; spikelets slender, acuminate, not indurate; plants generally aquatic:
Lemma narrowly acuminate, scabrid on veins .. Hymenachne amplexicaulis (Rudge) Nees Lemma acute to blunt, usually glabrous Sacciolepis striata (L.) Nash Inflorescence racemose; spikelets indurate; plants not aquatic:
Blades less than 20 cm long; spikelets in groups of 4 on a short stipe, the rachis not cylindrical Anthephom hermaphrodita (L.) O. Kuntze Blades more than 20 cm long; spikelets paired on a thick, jointed, cylindrical rachis
Rottboellia exaltata (L.) L.f.
Inflorescence paniculate or of more than 1 raceme:
• Inflorescence of paired or digitate spikes or racemes or of racemes clustered very near apex;
racemes not both densely fuzzy-pubescent and subtended by narrow spathaceous bracts:
Spikelets with conspicuous awns, the awns often geniculate:
Florets on spikes, the spikes several, digitate, not merely closely aggregated at apex;
spikelets with 1 fertile floret and a rudiment of several sterile lemmas Chloris Florets on racemes, the racemes paired or several merely closely aggregated at apex but
not digitate:
Racemes merely crowded at apex of inflorescence, not paired; spikelet with a promi- nent, deep, round pit in the glume Bothriochloa pertusa (L.) A. Camus Racemes paired; spikelet without depression in the glume:
Racemes usually less than 3 cm long, pubescent throughout with reddish-brown tri- chomes; inflorescences many, diffuse on plant; peduncles mostly less than 6 cm long Hyparrhenia rufa (Nees) Stapf Racemes usually more than 3 cm long, nearly glabrous or pubescent with white tri-
chomes; inflorescences few; peduncles mostly more than 6 cm long Ischaemum
ly. GRAMINEAE 123 Spikelets without awns:
Spikelets 2 or more at each node of the rachis Digitaria Spikelets solitary at each node of the rachis:
Racemes digitate, 4-7 per inflorescence Cynodon dactylon (L.) Pers.
Racemes not digitate, paired or congested near apex:
Spikelets of 3 or more florets each Eleusine indica (L.) Gaertn.
Spikelets of 1 floret each:
Spikelets 2 or more times as long as broad, acute at apex; at least some inflores- cences with other racemes below the apical pair Axonopus compressus (Sw.) Beauv.
Spikelets less than 2 times as long as broad, usually rounded or blunt at apex;
most inflorescences with a single pair of racemes:
Spikelets usually less than 2 mm long, with long, fine, white trichomes on mar- gin; plants stoloniferous Paspalum conjugatum Bergius Spikelets usually more than 3 mm long, the margins glabrous; plants rhizom-
atous Paspalum notatum Flugge Inflorescence paniculate or racemose with the racemes not clustered near the apex of the pe-
duncle; racemes densely fuzzy-pubescent (the trichomes longer than spikelets) and sub- tended by narrow spathaceous bracts:
• Spikelets conspicuously awned or long-acuminate, appearing awned, or subtended by long bristles and/or the inflorescence conspicuously long-pubescent, having an overall fuzzy appearance:
Leaf blades mostly more than 30 cm long:
Spikelets subtended by long firm bristles Setaria Spikelets not subtended by long firm bristles (sometimes with tufts of silky trichomes):
Blades more than 1 cm wide; plants usually aquatic or growing near water (at least on BCI):
Blades more than 1 m long and 4 cm wide; panicles usually more than 1 m long Gynerium sagittatum (Aubl.) Beauv.
Blades usually less than 75 cm long and 3.5 cm wide; panicles usually less than 60 cm long:
Spikelets not indurate, not awned but the lemma long-acuminate; lemma ± glabrous, spreading at maturity to expose long silky trichomes; frequent on shore Phragmites australis (Cav.) Trin.
Spikelets indurate, ridged, awned; lemma hispidulous, not spreading at matu- rity, without long silky trichomes; rare or absent from BCI Oryza latifolia Desv.
Blades mostly less than 1 cm wide; plants aquatic or terrestrial:
Spikelets awnless:
Inflorescence branched once, usually much longer than broad, the branches (racemes) floriferous to the base; plants ca 4 m tall; racemes with tufts of trichomes 1 cm or more long at base of spikelets; racemes not arising from persistent sheaths Saccharum Inflorescence branched many times, nearly as broad as long, the branches long,
floriferous only at apex; plants usually less than 1.5 m tall; racemes with scattered trichomes usually less than 1 cm long; racemes arising from per- sistent sheaths Andropogon hicomis L.
Spikelets awned:
Racemes not arising from spathes; trichomes at base of spikelets much shorter than spikelets Bothriochloa intermedia (R. Br.) A. Camus Racemes arising from (and often partially enveloped at base by) conspicuous
narrow spathes; trichomes at base of spikelets usually much longer than the spikelets:
Racemes scattered in a long loose inflorescence; spathes usually longer than the racemes; uhimate branches glabrous or nearly so just below the spathes Andropogon virginicus L.
Racemes aggregated in a dense compound inflorescence; spathes often shorter than the racemes and obscured by them; ultimate branches densely vil-
lous just below the spathes Andropogon glomeratus (Walt.) B.S.P.
Leaf blades mostly less than 30 cm long:
® Inflorescence less than 6 cm long or of few (usually less than 8) widely spaced racemes each less than 4 cm long:
• Spikelets conspicuously awned, the awns many times longer than spikelets:
Leaf blades mostly less than 5 mm wide, the awns geniculate and twisted Schizachyrium brevifolium Kunth Leaf blades mostly more than 5 mm wide, the awns ± straight Oplismenus
• Spikelets not conspicuously awned (glumes usually long-acuminate):
Inflorescence with silky pubescence much longer than spikelets; fruits not white and shiny Andropogon leucostachyus H.B.K.
Inflorescence glabrous or inconspicuously pubescent; fruits white and shiny:
Plants less than 60 cm tall; terminal inflorescence entirely staminate or want- ing, the axillary inflorescences each with 1 pistillate spikelet and several staminate spikelets about as long as the pistillate and arising from nearly the same point; fruits truncate at apex, solitary Lithachne pauciflora (Sw.) Poir.
Plants 1.5-5 m tall; inflorescences terminal or upper axillary, each branch with a single pistillate spikelet and with several much shorter staminate ones on branches below; fruits acute at apex Olyra latifolia L.
© Inflorescence more than 6 cm long, not of widely spaced racemes:
Plants of the forest; inflorescence not conspicuously pubescent to the naked eye, not feathery in appearance:
Petioles very short; blades lacking cross-veins; spikelets on short branches usually less than 3 cm long; glumes very long-acuminate, often 1-2 cm long; fruits white, shiny, indurate Olyra latifolia L.
Petioles usually 1-3 cm long; blades with conspicuous cross-veins; spikelets near the ends of slender branches usually more than 6 cm long; glumes merely acuminate; fruits inconspicuous Orthodada laxa (L. C. Rich.) Beauv.
Plants of clearings or lakeshores; inflorescence conspicuously pubescent, ± feathery:
Plants usually 2 m or more tall; racemes 15-30 cm long, not emerging from nar- row persistent spathes; spikelets very numerous, not awned, borne in 2 rows on 1 side of a flattened rachis Paspalum saccharoides Nees Plants 1-1.5 m tall; racemes usually less than 10 cm long, emerging from slender,
persistent spathes; spikelets few, awned, borne on a slender, terete, broadly sinuate rachis Schizachyrium microstachyum (Desv.) Roseng., Arr. & Izag.
Spikelets neither conspicuously awned nor long-acuminate so as to appear awned; inflores- cence not conspicuously long-pubescent and therefore not having an overall fuzzy appearance:
• Inflorescence with primary lateral branches strictly racemose or with slender, ± uni- form, raceme-like panicles (the inflorescence thus at least appearing 1-pinnate):
Uppermost primary lateral branches of inflorescence paired or digitate (arising from same point at apex of inflorescence):
Spikelets solitary at each node of rachis Axonopus compressus (Sw.) Beauv.
Spikelets paired at each node of rachis Digitaria Uppermost primary lateral branches not digitate:
Spikelets with 3 or 4 florets; lemmas conspicuously flattened, imbricate, ciliate on inner margin, sometimes awned Leptochloa virgata (L.) Beauv.
Spikelets with 1 floret, convex on at least 1 side; lemmas not ciliate or awned:
Spikelets ± ellipsoid (broadest at or near middle) to obovoid, mostly obtuse to rounded at apex (acute at apex in Paspalum repens), convex on one side, flat- tened on the other {Brachiaria mutica may appear convex/flat but is not) ...
Paspalum Spikelets ± ovoid, acute at apex, convex on both sides:
Leaf blades ovate-lanceolate, less than 5 cm long; spikelets with 2 or more light, pinpoint-size glands on the sterile lemma Panicum pulchellum Raddi Leaf blades ± linear, mostly more than 5 cm long; spikelets lacking crateri-
form glands:
Rachis or pedicel with hispid trichomes ca 1 mm long:
Spikelet less than 1.5 mm long; primary lateral branches strictly racemose, the rachis with hispid pubescence among spikelets Panicum, pilosum Sw.
Spikelets more than 2 mm long; primary lateral branches appearing race- mose but spikelets borne on very short secondary branches, these with sparse, long, stiff trichomes Brachiaria mutica (Forssk.) Stapf Rachis and pedicel lacking long-hispid pubescence:
Rachis with wing broader than width of spikelets ... Paspalum repens Bergius Rachis wingless or wing narrower than width of spikelets:
Spikelets less than 1.5 mm long, usually 2 or more at each node of ra- chis, ± spreading from slender rachis Panicum milleflorum Hitchc. & Chase Spikelets more than 2 mm long, solitary at each node of rachis, closely
fitted into winged sinuous rachis Paspalidium geminatum Stapf
ly. GRAMINEAE 12$
A Inflorescence with branches compounded 2 or more times, diffuse, open, lacking dis- tinctly racemose branches:
Blades distinctly long-petiolate above sheath, with prominent cross-veins when dry:
Spikelets green, uniform (all bisexual), borne near apex of very slender branches;
blades mostly less than 17 cm long; fruits enclosed, not emerging, essentially glabrous Orthodada laxa (L. C. Rich.) Beauv.
Spikelets brown, unisexual (staminate and much larger pistillate spikelets paired at nodes); blades more than 15 cm long; fruits densely pubescent at apex, emerging Pharus Blades lacking petiole above sheath, lacking cross-veins:
Plants with stout culms, erect, usually more than 1.5 m tall, usually unbranched:
Blades cordate-clasping at base Lasiacis procerrima (Hack.) Hitchc.
Blades not cordate-clasping at base:
Fruits not at all transversely rugose; ligule glabrous or only shallowly fringed at apex, the cilia scarcely longer than the ligule itself; plants aquatic:
Blades less than 40 cm long and 3 cm wide; spikelets obovate to subglobose, more than 2 mm wide Panicum mertensii Roth Blades to 1 m long and 6 cm wide; spikelets oblong-elliptic, less than 1 mm
wide Panicum grande Hitchc. & Chase Fruits at least weakly transversely rugose; ligule long ciliate from below the
apex, the cilia at least twice as long as the ligule itself; plants usually in clearings:
Blades plicate, more than 3 cm wide Setaria paniculifera (Steud.) Fourn.
Blades not plicate, less than 3 cm wide Panicum maximum Jacq.
Plants mostly less than 1 m tall or vinelike and clambering:
Plants with stout, ± woody culms, clambering; spikelets ± round; second glume and lemmas with a tuft of woolly trichomes at apex Lasiacis Plants not with stout, ± woody culms, clambering or erect; spikelets round or
not, lacking tufts of trichomes:
Mature spikelets purplish:
Plants aquatic; spikelets strongly hispid-ciliate, lacking glumes Leersia hexandra Sw.
Plants not aquatic; spikelets glabrous, not ciliate, having glumes Panicum fasciculatum Sw.
Mature spikelets green:
Spikelets with several flowers, more than 6 times as long as wide; lemmas long-ciliate; small, creeping to erect plant Ichnanthus Spikelets with 1 fertile flower, usually less than 3 times as long as wide; lem-
mas not long-ciliate:
Spikelets more than 3 mm long:
Spikelets having second glume and sterile lemma laterally compressed and keeled at apex; fruits white, with a small, usually green crest at apex; usually found in moist, open areas .... Acroceras oryzoides Stapf Spikelets not laterally compressed and keeled only at apex; fruits white
or tan, lacking a crest:
Spikelets glabrous on glumes (i.e., on outside), villous near margin of lemmas; fruits inconspicuous, lacking scars or wings near base Homolepis aturensis (H.B.K.) Chase Spikelets having glumes minutely scabrid on keel, often throughout,
the lemmas glabrous; fruits exposed at maturity, tan, bearing scars or narrow wings near base (a continuation from the rachilla or secondary axis of the inflorescence) Ichnanthus Spikelets less than 2 mm long:
• Plants inhabiting marshes, floating islands, ditches, wet thickets, or sandbars at the margin of the lake:
Leaf blades less than 5 cm long; spikelets obovate, blunt at apex;
glumes frequently pubescent; fruits plano-convex, densely pu- bescent Isachne polygonoides (Lam.) Doell Leaf blades mostly more than 5 cm long; spikelets ellipsoid to nar-
rowly ovoid, acute at apex; glumes glabrous; fruits glabrous:
Spikelets borne on long, slender stalks, 5 mm or more long Panicum trichanthum Nees Spikelets borne on short stalks, seldom more than 1-2 mm long ...
Panicum polygonatum Schult.
MONOCOTYLEDONEAE
* Plants not inhabiting marshes or other wet areas, usually in clearings:
Leaf blades linear, usually 15 cm or more long, very narrow Sporoholus indicus (L.) R. Br.
Leaf blades less than 12 cm long:
Spikelets ca 1 mm long on pedicels 3 mm or more long; blades nar- rowly ovoid, less than 7 cm long, to 1.5 cm wide Panicum trichoides Sw.
Spikelets 1.5-2 mm long on pedicels less than 1.5 mm long; blades linear-lanceolate, to 12 cm long and 12 mm wide Panicum polygonatum Schult.
to feed on pollen. Paspalum virgatum is probably polli- nated by small noctuid moths, which visit plants in the evening apparently for the sticky, sweet fluid present at the time of flowering (Karr, 1976). In Costa Rica, Pani- cum fasciculatum and P. laxum Sw. are heavily visited by the bees Trigona, Augochloropsis (Halictidae), and Caenaugochlora (Halictidae) (R. Heithaus, pers. comm.).
It could be expected that other species that occur deep in the forest, where wind currents are poor in the dry season, are also insect pollinated. On the other hand Pharus, which may occur in dense forest, is believed to be wind pollinated (G. Davidse, pers. comm.). Fewer than 15 grass species are restricted to the forest, of which only the bamboos (including Rhipidocladum and Ckus- quea), which rarely flower, and Pharus, Streptochaeta, and Streptogyne usually occur in dense, unopened forest.
The remainder, including Lithachne, Orthoclada, Olyra, Ichnanthus, and Panicum pulchellum, are generally found in open areas or along trails, where wind pollination may be eff'ective. Except for Lithachne, which may be insect pollinated, the species of open areas flower principally in the dry season, when winds are greatest.
Most species occur in clearings. The flowers of Lasiacis open between 7:30 and 9:30 A.M., but insect visitors have never been seen (G. Davidse, pers. comm.) so the flowers are apparently wind pollinated.
Grasses are far more diverse in diaspore strategy than in their pollinating agents. Wind plays a principal role (van der Pijl, 1968), especially for those taxa with plumed spikelets or feathery inflorescences such as Andropogon, Schizachyrium, Gynerium, Saccharum, Paspalum saccha- roides, Bothriochloa, and Phragmites. In addition to these, many other species have small disarticulating spikelets or inflorescence parts that are probably also in part wind dispersed.
Small birds disperse the seeds of many species, partic- ularly those with larger or more attractive spikelets, in- cluding Oryza and most of the panicoid grasses, as well as species with attractive fruits such as Lithachne, Olyra, and especially Lasiacis. Investigations by Davidse and Morton (1973) showed that many fruit-eating birds eat the spikelets of Lasiacis in great numbers. The glumes contain relatively large amounts of oil, which provides nourishment for the birds, and the caryopsis passes through the bird unharmed. Birds no doubt eat the fruits of a wide variety of grass species, but in general it is uncertain what percentage of the seeds pass through the gizzard unharmed. Ridley (1930) suggested that some seeds may be picked up by birds from the ground as they
look for grit for their gizzard. Enders (1935) reported that iguanas eat Brachiaria mutica and Panicum grande.
Elsewhere many grasses are dispersed by herbivores, which swallow the seeds while grazing and regurgitate or pass them unharmed (Ridley, 1930). Eleusine indica and Cynodon dactylon, both grasses of clearings, have their seeds carried by ants (Ridley, 1930; Wheeler, 1910).
A number of grasses are adapted for epizoochorous dispersal by appendages on the spikelets. These include
Cenchrus, Pharus, Streptochaeta, and Streptogyne, and probably Paspalum conjugatum, Oplismenus, Leersia, Oryza, Chloris, Orthoclada, and most species with feath- ery, disarticulating inflorescences. The awn or awnlike structure of Oplismenus, Oryza, and Chloris probably serves as much in ensuring disarticulation of the spikelet as in dispersal. Plants of many other species also have prominently geniculate and twisted awns, such as Hypar- rhenia, Ischaemum, Polytrias, Schizachyrium, and Both- riochloa. These probably function in part in epizoochorous dispersal and perhaps also for implantation, such as in the well-known case of Stipa.
Those taxa that are restricted to aquatic habitats along the shore probably rely in part on dispersal by water cur- rents. These include Hymenachne, Isachne, Leersia, Oryza, Brachiaria, Panicum grande, P. mertensii, P. milleflorum, P. polygonatum, P. trichanthum, Paspalidium geminatum, Paspalum repens, and Phragmites.
Unlike most forest species, such as trees with seeds that germinate soon after falling, grasses have seeds that may remain dormant for considerable periods (Corner, 1964).
Some 620-700 genera and 10,000 species; distributed worldwide.
ACROCERAS Stapf
Acroceras oryzoides Stapf in Prain, Fl. Trop. Africa 9:622. 1920
Panicum zizanoides H.B.K.
Perennial, mostly 0.5-1.5 (2) m tall, decumbent-spreading, rooting at lower nodes. Sheaths shorter than the inter- nodes, glabrous or hispid near apex; blades mostly 5-15 cm long, 1-2 (3) cm wide, acuminate, cordate-clasping at the base, the margin white and scabrid sometimes with submarginal hispid trichomes. Inflorescence a sparsely branched panicle, mostly terminal, 10-20 cm long; spike- lets paired, narrowly acuminate at apex, rather widely spaced, appressed, 5-6 mm long, glabrous, each pair unequally short-pedicellate; pedicels flattened, scabrid;