The grass genera of the world
Habit, vegetative morphology. Perennial; geniculate ascending, rooting at the nodes. Culms 15–80 cm high; herbaceous; branched above. Culm nodes hairy, or glabrous. Culm internodes hollow. Young shoots intravaginal. Leaves not basally aggregated; non-auriculate. Leaf blades linear; narrow; 3–5 mm wide; flat; without cross venation; persistent. Ligule present; a fringed membrane (very narrow), or a fringe of hairs; about 0.3 mm long. Contra-ligule present (a line of hairs).
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets all alike in sexuality (but sometimes with cleistogamous spikelets lacking bristles at the base of the inflorescence). Plants with hidden cleistogenes. The hidden cleistogenes in the leaf sheaths (the upper sheaths).
Inflorescence. Inflorescence a false spike, with spikelets on contracted axes (loosely spicate, with appressed, deciduous, one-spikeleted racemelets). Inflorescence axes not ending in spikelets (the racemelet ending in the bristle, which subtends the spikelet and extends beyond it). Inflorescence espatheate; not comprising partial inflorescences and foliar organs. Spikelet-bearing axes very much reduced (to the long, pungent stipe, one spikelet and its subtending bristle); disarticulating; falling entire (i.e., the racemelets disarticulating, complete with spikelet and bristle, and contributing a pointed callus beneath the spikelet). Spikelets subtended by solitary bristles. The bristles deciduous with the spikelets. Spikelets solitary (one per racemelet); not secund; subsessile.
Female-fertile spikelets. Spikelets 8–13 mm long; abaxial; compressed dorsiventrally; falling with the glumes (and the racemelet); with conventional internode spacings. Rachilla terminated by a female-fertile floret. Hairy callus absent. Callus long (constituted by the proximal part of the branch beneath the spikelet); pointed.
Glumes two; minute; more or less equal; shorter than the spikelets; shorter than the adjacent lemmas; dorsiventral to the rachis; hairless; not pointed; awnless; non-carinate; similar (hyaline). Lower glume 0 nerved. Upper glume 0 nerved. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. The proximal incomplete florets 1; epaleate; sterile. The proximal lemmas awnless (but acuminate-subulate); 7–11 nerved (these anastomosing above); more or less equalling the female-fertile lemmas; similar in texture to the female-fertile lemmas (firmly membranous); not becoming indurated.
Female-fertile florets 1. Lemmas decidedly firmer than the glumes; smooth; not becoming indurated; entire; pointed; awnless (but acuminate-subulate, like the L1); hairless; glabrous; non-carinate; having the margins lying flat on the palea; without a germination flap; 7 nerved. Palea present; relatively long (about equalling the lemma); entire; awnless, without apical setae; textured like the lemma; not indurated; 2-nerved (linear-lanceolate, acuminate, membranous); keel-less (abaxially rounded). Lodicules present; 2; free; fleshy; glabrous; not or scarcely vascularized. Stamens 3. Anthers 2.5 mm long; not penicillate; without an apically prolonged connective. Ovary apically glabrous. Styles fused. Stigmas 2; white.
Fruit, embryo and seedling. Fruit compressed dorsiventrally. Hilum short. Embryo large.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells similar in shape costally and intercostally. Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; panicoid-type; 57–63–66 microns long; 4.5–5.4–6 microns wide at the septum. Microhair total length/width at septum 9.5–14.7. Microhair apical cells 30–34.5 microns long. Microhair apical cell/total length ratio 0.52–0.6. Stomata common; (24–)27–28.5(–33) microns long. Subsidiaries low dome-shaped (mostly), or triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs. Costal short-cells conspicuously in long rows. Costal silica bodies panicoid-type; mostly dumb-bell shaped; not sharp-pointed.
Transverse section of leaf blade, physiology. C4; XyMS. Mesophyll with non-radiate chlorenchyma. Leaf blade nodular in section; with the ribs more or less constant in size. Midrib conspicuous; having a conventional arc of bundles; with colourless mesophyll adaxially. Bulliforms present in discrete, regular adaxial groups to not present in discrete, regular adaxial groups; occasionally in simple fans (but the epidermis largely irregularly bulliform). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; nowhere forming figures. Sclerenchyma all associated with vascular bundles.
Classification. Watson & Dallwitz (1994): Panicoideae; Panicodae; Paniceae. Soreng et al. (2015): Panicoideae; Panicodae; Paniceae; Cenchrinae. 2 species.
Distribution, phytogeography, ecology. Africa, Madagascar, Cuba, Brazil.
Commonly adventive. Hydrophytic, or helophytic; species of open habitats; glycophytic. Swamps and lakes.
References, etc. Leaf anatomical: this project.
Illustrations. • P. prostrata: Jacques-Félix, 1962. • P. prostrata: Hitchcock (1936)
We advise against extracting comparative information from the descriptions. This is much more easily achieved using the DELTA data files or the interactive key, which allows access to the character list, illustrations, full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, distributions of character states within any set of taxa, geographical distribution, and classifications. See also Guidelines for using data taken from Web publications.
Cite this publication as: ‘Watson, L., Macfarlane, T.D., and Dallwitz, M.J. 1992 onwards. The grass genera of the world: descriptions, illustrations, identification, and information retrieval; including synonyms, morphology, anatomy, physiology, phytochemistry, cytology, classification, pathogens, world and local distribution, and references. Version: 13th November 2017. delta-intkey.com/grass’.