The grass genera of the world
Habit, vegetative morphology. Perennial; conspicuously stoloniferous and caespitose. Culms 3–11 cm high; herbaceous; unbranched above. Culm nodes sparsely or densely hairy. Leaves mostly basal. Leaf blades narrow; 0.2–0.5 mm wide (and 1.5–4 cm long); rolled (involute); without abaxial multicellular glands; not pseudopetiolate; without cross venation. Ligule present; an unfringed membrane (apically erose).
Reproductive organization. Plants dioecious; without hermaphrodite florets. The spikelets all alike in sexuality (on the one plant); female-only, or male-only. Plants outbreeding.
Inflorescence. Inflorescence few spikeleted; a cluster of 2–4 appressed spikelets, the males long exserted, the females sessile among the upper leaf sheaths; digitate, or non-digitate (?); espatheate; not comprising partial inflorescences and foliar organs. Spikelet-bearing axes persistent.
Female-sterile spikelets. Male spikelets 2–4 appressed, in exserted inflorescences 0.5–1.5 cm long. Spikelets 5–13 mm long, laterally compressed, glabrous, with 3–8 florets; palea glabrous, equalling the lemma; stamens 3, unequal. Rachilla of male spikelets prolonged beyond the uppermost male floret. The male spikelets with glumes; 3–8 floreted. Male florets 3 staminate.
Female-fertile spikelets. Spikelets 5–11 mm long; compressed laterally; tardily disarticulating above the glumes; disarticulating between the florets. Rachilla prolonged beyond the uppermost female-fertile floret; the rachilla extension with incomplete florets.
Glumes two; very unequal; shorter than the spikelets; shorter than the adjacent lemmas; hairy (at the base only - glabrous above); pointed; awnless; similar (obovate-lanceolate). Lower glume indistinctly 2–8 nerved. Upper glume indistinctly 8 nerved. Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets. The distal incomplete florets merely underdeveloped.
Female-fertile florets 3–8. Lemmas broad at the base, narrowing above; not becoming indurated; entire; pointed; awnless; hairy (densely pilose at the base, glabrous above); 10–13 nerved. Palea present; relatively long (broadened and hairy at the base); convolute around the flower; awnless, without apical setae; not indurated. Lodicules present; fleshy (small); glabrous (?). Stamens 0. Ovary apically glabrous. Stigmas 2.
Fruit, embryo and seedling. Fruit ellipsoid; hairy on the body (hairs about 2/5 as long as the fruit); smooth (?). Hilum short. Pericarp fused.
Abaxial leaf blade epidermis. Papillae present; costal and intercostal. Intercostal papillae consisting of one symmetrical projection per cell. Mid-intercostal long-cells rectangular. Microhairs present; more or less spherical; ostensibly one-celled; chloridoid-type (often somewhat sunken). Stomata common. Intercostal short-cells not paired. Intercostal silica bodies absent. Costal short-cells neither distinctly grouped into long rows nor predominantly paired. Costal silica bodies present throughout the costal zones to confined to the central file(s) of the costal zones; rounded to saddle shaped; not sharp-pointed.
Transverse section of leaf blade, physiology. Lamina mid-zone in transverse section open.
C4; XyMS+. PCR sheaths of the primary vascular bundles complete. PCR sheath extensions absent. Mesophyll with radiate chlorenchyma; traversed by columns of colourless mesophyll cells. Leaf blade with distinct, prominent adaxial ribs. Midrib not readily distinguishable; with one bundle only. Bulliforms not present in discrete, regular adaxial groups. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders absent (there being no adaxial sclerenchyma). Sclerenchyma not all bundle-associated. The extra sclerenchyma in abaxial groups (there being some sclerification of colourless cells in the abaxial furrows). The lamina margins with fibres.
Special diagnostic feature. Panicle loose, or if dense then interrupted, neither cylindrical nor ovoid: awns usually present, usually twisted, usually distinctly dorsal, conspicuous if inflorescence compact.
Cytology. 2n = 38.
Classification. Watson & Dallwitz (1994): Chloridoideae; main chloridoid assemblage. Soreng et al. (2015): Chloridoideae; Cynodonteae; Monanthochloinae. 1 species (R. eludens).
Distribution, phytogeography, ecology. Mexico.
Xerophytic; species of open habitats; halophytic (alkali flats).
References, etc. Morphological/taxonomic: Soderstrom and Decker 1964. Leaf anatomical: Van den Borre 1994; studied by us - iR. eludens Soderstrom & Decker.
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’.