The grass genera of the world
Habit, vegetative morphology. Perennial; caespitose. Culms 15–40 cm high; herbaceous; unbranched above. Culm nodes hairy. Leaves mostly basal; non-auriculate. Leaf blades narrow (slender); rolled (involute); without cross venation; persistent.
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets.
Inflorescence. Inflorescence paniculate; contracted (rather narrow, 3–6 cm long); espatheate; not comprising partial inflorescences and foliar organs. Spikelet-bearing axes persistent. Spikelets pedicellate.
Female-fertile spikelets. Spikelets 3–4 mm long; compressed laterally; falling with the glumes. Rachilla terminated by a female-fertile floret. Hairy callus absent (?).
Glumes present; two; very unequal; (the upper) shorter than the spikelets to about equalling the spikelets (the upper about half as long); the upper shorter than the adjacent lemmas to long relative to the adjacent lemmas (sometimes little shorter than the spikelet); hairless; awned (both long-awned from between the lobes of the bifid apex); carinate; firmly membranous. Lower glume strongly 3 nerved, or 5 nerved. Upper glume strongly 5 nerved. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. Spikelets with proximal incomplete florets. The proximal incomplete florets 1; sterile. The proximal lemmas awned (shortly, from the apical notch), or awnless (but then mucronate); 3 nerved; decidedly exceeding the female-fertile lemmas; decidedly firmer than the female-fertile lemmas (similar to the glumes).
Female-fertile florets 1. Lemmas less firm than the glumes; thin; not deeply cleft; awnless, or mucronate (the nerve excurrent from the keel); carinate; without a germination flap; 5 nerved (with 2 pairs of obscure laterals). Palea absent. Lodicules absent (?). Stamens 2.
Fruit, embryo and seedling. Fruit ellipsoid; compressed dorsiventrally.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells similar in shape costally and intercostally (but the costals smaller and narrower); of similar wall thickness costally and intercostally (walls of medium thickness). Mid-intercostal long-cells rectangular; having markedly sinuous walls (pitted). Microhairs present; panicoid-type; 48–54–60 microns long; (9–)9.3–9.9(–10.2) microns wide at the septum. Microhair total length/width at septum 4.8–6.7. Microhair apical cells (27–)33–36(–39) microns long. Microhair apical cell/total length ratio 0.56–0.67. Stomata common; 27(–30) microns long. Subsidiaries triangular; including both triangular and parallel-sided forms on the same leaf. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs; silicified. Intercostal silica bodies crescentic. Costal short-cells predominantly paired. Costal silica bodies rounded (a few), or tall-and-narrow (very few), or crescentic (predominating); not sharp-pointed.
Transverse section of leaf blade, physiology. C4; XyMS. Mesophyll without adaxial palisade. Leaf blade with distinct, prominent adaxial ribs; with the ribs more or less constant in size (round-topped). Midrib not readily distinguishable; with one bundle only; with colourless mesophyll adaxially (each rib with an adaxial group of large colourless cells). Bulliforms present in discrete, regular adaxial groups; in simple fans (these small, in each furrow). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders absent (each bundle with a wide, narrow adaxial strand and an abaxial girder). Sclerenchyma all associated with vascular bundles.
Classification. Watson & Dallwitz (1994): Panicoideae; Panicodae; Paniceae (Arthropogoneae). Soreng et al. (2015): Panicoideae; Panicodae; Paspaleae. 1 species (R. filiformis).
Distribution, phytogeography, ecology. West Indies.
Mesophytic; species of open habitats. Savanna, palm barrens, bushy slopes.
References, etc. Leaf anatomical: studied by us.
Special comments. Fruit data wanting. Illustrations. • R. filiformis: Kunth (1835). • R. filiformis: 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: 11th December 2017. delta-intkey.com/grass’.