The grass genera of the world
Habit, vegetative morphology. Annual; decumbent (mat-forming). Culms 20–30 cm high; herbaceous; branched above. Leaves not basally aggregated; non-auriculate. Leaf blades lanceolate; narrow; 2–5 mm wide; cross veined. Ligule a fringed membrane (very narrow), or a fringe of hairs.
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets (the lower floret hermaphrodite, the upper female-only).
Inflorescence. Inflorescence of spicate main branches (a panicle of short, unilateral spikes). Inflorescence axes not ending in spikelets (the rachides ending in blunt naked tips). Inflorescence espatheate; not comprising partial inflorescences and foliar organs. Spikelet-bearing axes persistent. Spikelets secund; biseriate; contiguous.
Female-fertile spikelets. Spikelets 1.7–2.3 mm long; abaxial; compressed dorsiventrally; disarticulating above the glumes; disarticulating between the florets. Rachilla terminated by a female-fertile floret. Hairy callus absent.
Glumes two; more or less equal; shorter than the adjacent lemmas; hairless; pointed; awnless; similar (firmly membranous, with hyaline margins). Lower glume 4–7 nerved. Upper glume 4–7 nerved. Spikelets with female-fertile florets only.
Female-fertile florets 2 (but the upper usually female-only, much shorter and blunter). Lemmas similar in texture to the glumes to decidedly firmer than the glumes (papery); becoming indurated (L1), or not becoming indurated (L2); entire; pointed (L1 acuminate), or blunt (L2 obtuse to subacute); awnless; hairy; non-carinate; having the margins inrolled against the palea; with a clear germination flap; 5 nerved. Palea present; relatively long; entire, or apically notched (slightly); awnless, without apical setae; not indurated; 2-nerved. Lodicules present; 2; free; fleshy; glabrous. Stamens 3. Ovary apically glabrous. Styles free to their bases. Stigmas 2.
Fruit, embryo and seedling. Fruit small; slightly compressed dorsiventrally. Hilum short. Embryo large. Endosperm containing only simple starch grains. Embryo without an epiblast; with a scutellar tail; with an elongated mesocotyl internode.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present. Intercostal zones without typical long-cells (these being cubical). Mid-intercostal long-cells having straight or only gently undulating walls. Microhairs present; panicoid-type; 15–22 microns long. Microhair apical cells 9–16 microns long. Microhair apical cell/total length ratio 0.68. Stomata common. Subsidiaries parallel-sided to triangular; including both triangular and parallel-sided forms on the same leaf. Intercostal short-cells absent or very rare. Costal short-cells conspicuously in long rows. Costal silica bodies acutely-angled; sharp-pointed.
Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with radiate chlorenchyma; Isachne-type. Leaf blade with distinct, prominent adaxial ribs; with the ribs more or less constant in size. Midrib not readily distinguishable; with one bundle only. Bulliforms present in discrete, regular adaxial groups (in the furrows); in simple fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present. Sclerenchyma all associated with vascular bundles.
Classification. Watson & Dallwitz (1994): Panicoideae; Panicodae; Isachneae. Soreng et al. (2015): Micrairoideae; Isachneae. 1 species (H. guineensis).
Distribution, phytogeography, ecology. Tropical Africa.
Helophytic (swamps and shallow water).
References, etc. Leaf anatomical: Metcalfe 1960.
Illustrations. • H, guineensis, as H. isachnoides: Hook Ic. Pl. 30 (1913). • H. guineensis: Jacques-Félix, 1962
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: 11th December 2017. delta-intkey.com/grass’.