The grass genera of the world
Habit, vegetative morphology. Perennial; stoloniferous. Culms 60–100 cm high (standing 30–40 cm above the water); herbaceous; branched above. Culm nodes glabrous. Culm internodes hollow. Plants unarmed. Young shoots intravaginal. Leaves not basally aggregated; non-auriculate. Leaf blades linear, or linear-lanceolate; narrow; to 9 mm wide; flat, or rolled; without cross venation; persistent. Ligule an unfringed membrane to a fringed membrane; truncate (entire or laciniate); 1–1.5 mm long. Contra-ligule absent.
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets all alike in sexuality.
Inflorescence. Inflorescence a false spike, with spikelets on contracted axes, or a single raceme (a coarse, cylindrical raceme, apparently representing a raceme of reduced glomerules, each glomerule shortly pedunculate, comprising a single spikelet subtended by a lobed scale forming an involucre-plus-bristle). Inflorescence morphologically difficult - comparable with that of Anthepora, Cenchrus or Pseudoraphis?. Inflorescence espatheate (but enveloped below by the uppermost leaf sheath, whose blade is at least as long as the inflorescence); not comprising partial inflorescences and foliar organs. Spikelet-bearing axes very much reduced (each reduced to one spikelet, with a herbaceous, lobed scale and bristle); disarticulating; falling entire (i.e., the reduced glomerules deciduous - the main axis persistent). Spikelets associated with bractiform involucres and subtended by solitary bristles (each spikelet with a purplish, irregularly 4–6 lobed involucre, this being herbaceous except for one lobe, which is almost free, awnlike, scabrid and 12–25 mm long). The bristles deciduous with the spikelets. The involucres shed with the fertile spikelets. Spikelets solitary; not secund; sessile.
Female-fertile spikelets. Spikelets 10–14 mm long; abaxial; compressed dorsiventrally; falling with the glumes; not disarticulating between the florets; with conventional internode spacings. Rachilla terminated by a female-fertile floret; hairless. Hairy callus absent. Callus absent.
Glumes one per spikelet (the G1 missing), or two; very unequal (the G1 when present very small); shorter than the spikelets; shorter than the adjacent lemmas (the G2 about half length of spikelet); free; dorsiventral to the rachis; hairless; pointed (G2 narrowly ovate); awnless. Lower glume much shorter than half length of lowest lemma; when present, 0 nerved. Upper glume 1–3 nerved (scarious). Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. The proximal incomplete florets 1; paleate. Palea of the proximal incomplete florets fully developed (as long as the lemma). The proximal incomplete florets male. The proximal lemmas awnless; 9 nerved; more or less equalling the female-fertile lemmas; less firm than the female-fertile lemmas (membranous).
Female-fertile florets 1. Lemmas decidedly firmer than the glumes (cartilaginous below, herbaceous above); smooth; not becoming indurated; entire; pointed; awnless (the tip caudate, membranous); hairless; glabrous; non-carinate; having the margins lying flat on the palea; without a germination flap; 7 nerved. Palea present; relatively long (equalling the lemma); tip caudate; textured like the lemma; 2-nerved; keel-less (dorsally rounded). Palea back glabrous. Lodicules absent. Stamens 3. Anthers 5.5 mm long; not penicillate; without an apically prolonged connective. Styles fused (to the bases of the stigmas). Stigmas 2; red pigmented.
Fruit, embryo and seedling. Fruit compressed dorsiventrally. Embryo large (about 1/3 the length of the fruit).
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present; costal and intercostal. Intercostal papillae consisting of one oblique swelling per cell. Long-cells similar in shape costally and intercostally (but the costals rather smaller). Intercostal zones without typical long-cells (of more or less isodiametric cells). Mid-intercostal long-cells rectangular (mostly quite square); having markedly sinuous walls. Microhairs present; panicoid-type. Stomata seemingly absent or very rare. Costal short-cells conspicuously in long rows. Costal silica bodies panicoid-type; not sharp-pointed.
Transverse section of leaf blade, physiology. C4; XyMS+. PCR cell chloroplasts centrifugal/peripheral. Leaf blade with distinct, prominent adaxial ribs to nodular in section; with the ribs more or less constant in size (low, round-topped). Midrib conspicuous (very); having a conventional arc of bundles (a large median with about 8 smaller laterals on either side, all abaxial); with colourless mesophyll adaxially (the colourless mass with a lacuna in the centre). Bulliforms present in discrete, regular adaxial groups; associating with colourless mesophyll cells to form arches over small vascular bundles (in places, apparently). Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders present (with the primaries). Sclerenchyma all associated with vascular bundles.
Special diagnostic feature. The inflorescence a coarse, cylindrical raceme, apparently representing a raceme of reduced glomerules, each glomerule shortly pedunculate, comprising a single spikelet subtended crosswise by a lobed scale forming an involucre-plus-bristle.
Classification. Watson & Dallwitz (1994): Panicoideae; Panicodae; Paniceae. Soreng et al. (2015): Panicoideae; Panicodae; Paniceae; Cenchrinae. 1 species (O. abyssinicum).
Distribution, phytogeography, ecology. Abyssinia and southern Africa.
Helophytic (in flowing or standing water); species of open habitats; glycophytic.
References, etc. Morphological/taxonomic: Stapf 1916. Leaf anatomical: photos of O. abyssinicum provided by R.P. Ellis.
Illustrations. • O. abyssinicum: Hook. Ic. Pl. 31 (1916). • General aspect (O. abyssinicum): Gibbs Russell et al., 1990
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’.