The grass genera of the world
Habit, vegetative morphology. Delicate perennial (R. esenbeckii and perhaps R. minima), or annual (mostly); caespitose, or decumbent (sometimes mat-forming). The flowering culms leafy. Culms 5–30(–40) cm high; herbaceous; where recorded, only in R. vanessiae branched above. Rhizomes pachymorph. Plants unarmed. Leaves not basally aggregated; auriculate, or non-auriculate; without auricular setae. Leaf blades ovate, or elliptic (to ovate-triangular, often stringly asymmetrical and apiculate); flimsy (membranous), or neither leathery nor flimsy; narrow; 2.4–8(–11) mm wide (and only 4–15(-22 mm long); slightly to much asymmetric at their bases; pseudopetiolate; cross veined. Ligule an unfringed membrane, or a fringed membrane (?-membranous or membranous-ciliate); truncate; 0.2–0.5 mm long.
Reproductive organization. Plants monoecious with all the fertile spikelets unisexual; without hermaphrodite florets. The spikelets of sexually distinct forms on the same plant; female-only and male-only. The male and female-fertile spikelets in different inflorescences, or mixed in the inflorescence (in partial (syn)inflorescences which are axillary and all-female, terminal and all-male, or mixed). The spikelets overtly heteromorphic.
Inflorescence. Inflorescence determinate, or indeterminate (some species with synflorescences); few spikeleted; a scanty, racemelike panicle, sometimes reduced to two spikelets. Spikelet-bearing axes persistent. Spikelets not secund; pedicellate.
Female-sterile spikelets. Male spikelets shorter pedicelled than females, hyaline and early deciduous. Rachilla of male spikelets terminated by a male floret. The male spikelets without glumes; without proximal incomplete florets; 1 floreted. Male florets 1; 3 staminate.
Female-fertile spikelets. Spikelets 1.3–2.3(–2.7) mm long; elliptic; falling with the glumes (mostly), or disarticulating above the glumes (the glumes persistent in two species); with a characteristic, thickened and indurate interglumal internode. Rachilla terminated by a female-fertile floret. Callus absent.
Glumes two; more or less equal; about equalling the spikelets; long relative to the adjacent lemmas; hairless; pointed (acute); similar (membranous-herbaceous, with basal pulvini). Lower glume 3 nerved. Upper glume 3 nerved, or 5 nerved. Spikelets with female-fertile florets only.
Female-fertile florets 1. Lemmas decidedly firmer than the glumes (thinly leathery); smooth to papillose; becoming indurated (bony); entire; awnless; non-carinate; having the margins inrolled against the palea; with a clear germination flap. Palea present; tightly clasped by the lemma; awnless, without apical setae. Stamens 0. Styles fused. Stigmas 2.
Fruit, embryo and seedling. Fruit small; ellipsoid. Hilum short (punctiform, elliptic or short-linear). Embryo small.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present; costal and intercostal (abundant). Intercostal papillae several per cell (most long-cells with a single median row). Long-cells markedly different in shape costally and intercostally (the costals much narrower); of similar wall thickness costally and intercostally (thin walled). Mid-intercostal long-cells rectangular; having markedly sinuous walls (the sinuosity coarse). Microhairs present; elongated; clearly two-celled; panicoid-type; 34.5–42 microns long; 5.4–6.3 microns wide at the septum. Microhair total length/width at septum 6–7.8. Microhair apical cells 16.5–18 microns long. Microhair apical cell/total length ratio 0.4–0.5. Stomata common; 19.5–21 microns long. Subsidiaries papillate (two on each, but thin walled and relatively inconspicuous); predominantly triangular. Guard-cells overlapped by the interstomatals (slightly), or overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs; silicified. Intercostal silica bodies vertically elongated-nodular. Short, thick-walled macrohairs with simple bases common. Crown cells absent. Costal short-cells conspicuously in long rows. Costal silica bodies consistently oryzoid; not sharp-pointed.
Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with adaxial palisade; insufficiently well preserved to score for arm-cells, in the material seen; with fusoids. The fusoids external to the PBS. Leaf blade adaxially flat (and thin). Bulliforms present in discrete, regular adaxial groups (a large, wide group in every intercostal zone); in simple fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; forming figures (every bundle having a small I or anchor). Sclerenchyma all associated with vascular bundles.
Cytology. Chromosome base number, x = 10.
Classification. Watson & Dallwitz (1994): Bambusoideae; Oryzodae; Olyreae. Soreng et al. (2015): Bambusoideae; Bambusodae; Olyreae; Olyrinae. 7 species.
Distribution, phytogeography, ecology. West Indies and tropical America.
Helophytic; glycophytic. Damp depressions and wet rocks near waterfalls.
References, etc. Morphological/taxonomic: Maguire et al. 1965; Zuloaga and Judziewicz 1991. Leaf anatomical: studied by us - R. esenbeckiana (Steud.) Calderon & Soderstrom.
Special comments. Fruit data wanting. Illustrations. • R. lunata: V. dudás (1991), Ann. Miss. Bot. Gard. 78
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’.