The grass genera of the world
Type species: R. altera (Rendle) Chiov.
Habit, vegetative morphology. Perennial; densely caespitose (from a cushion of old, fibrous leaf sheaths). Culms 5–35 cm high; herbaceous; unbranched above. Culm nodes glabrous. Culm internodes solid. Plants unarmed. Young shoots intravaginal. Leaves mostly basal; non-auriculate. The basal sheaths persistent, densely woolly, fibrous when old. Leaf blades linear; narrow; to 0.7 mm wide; setaceous; folded (at the base, the adaxial surfaces adnate); without abaxial multicellular glands; without cross venation; persistent (but usually burned off annually). Ligule present; a fringed membrane (the membrane unusually firm); 0.2–0.3 mm long. Contra-ligule absent.
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets of sexually distinct forms on the same plant, or all alike in sexuality; hermaphrodite, or hermaphrodite and sterile (the uppermost 2–3 spikelets reduced).
Inflorescence. Inflorescence a single spike (to 5 cm long, rarely a pair of spikes). Inflorescence axes not ending in spikelets (their tips obtuse). Rachides flattened and winged (convex on back, with membranous, hairy margins). Inflorescence espatheate; not comprising partial inflorescences and foliar organs. Spikelet-bearing axes spikes; persistent. Spikelets solitary; secund; alternately biseriate; sessile; imbricate.
Female-fertile spikelets. Spikelets 4–5.5 mm long; adaxial; with the G1 compressed obliquely, the G2 compressed dorsiventrally; disarticulating between the glumes (disarticulating above the persistent G1, the G2 falling with and enveloping the florets); not disarticulating between the florets; with conventional internode spacings. Rachilla prolonged beyond the uppermost female-fertile floret; hairless; the rachilla extension with incomplete florets. Hairy callus present (small). Callus short; pointed.
Glumes two; more or less equal; exceeding the spikelets; long relative to the adjacent lemmas (both longer than the florets); lateral to the rachis; hairy (lanose, G2), or hairless (glabrous, G1); without conspicuous tufts or rows of hairs; obtuse, lanceolate-oblong; awnless; carinate (G1), or non-carinate (G2); very dissimilar (firmly membranous, the G1 obliquely laterally compressed, the G2 dorsally compressed). Lower glume 1 nerved. Upper glume 1 nerved. Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets. The distal incomplete florets 1; male or sterile, banana-shaped, hairless, the lemma shorter and thinner than the L1, the palea reduced or absent; awnless.
Female-fertile florets 1. Lemmas similar in texture to the glumes; not becoming indurated; incised; shortly 2 lobed; not deeply cleft; awnless; hairy (with dense, silky hairs on the keels); non-carinate (but rather, 3 keeled: laterally compressed, the margins beyond the lateral keels narrow, hyaline, infolded); without a germination flap; 3 nerved. Palea present; relatively long (slightly exceeding the lemma); apically notched; awnless, without apical setae (glabrous); thinner than the lemma; not indurated (hyaline-membranous); 2-nerved; 2-keeled. Palea keels wingless; minutely scabrous. Lodicules present (briefly joined to the base of the palea); 2; free; fleshy; glabrous. Stamens 3. Anthers 2.5 mm long; not penicillate; without an apically prolonged connective. Ovary apically glabrous (suppressed in the upper floret). Styles free to their bases. Stigmas 2; brown.
Fruit, embryo and seedling. Fruit free from both lemma and palea; small (2 mm long); ellipsoid; compressed dorsiventrally, or trigonous. Hilum short. Embryo small (seemingly, judging from immature material).
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells of similar wall thickness costally and intercostally (medium thick walled). Mid-intercostal long-cells rectangular; having markedly sinuous walls (and pitted). Microhairs present; more or less spherical; ostensibly one-celled (15 to 18 microns in diameter); chloridoid-type. Stomata common; 27–28.5–30 microns long. Subsidiaries high dome-shaped, or triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; not paired (solitary); not silicified. Intercostal silica bodies absent. Costal short-cells conspicuously in long rows. Costal silica bodies confined to the central file(s) of the costal zones; almost exclusively saddle shaped (large); not sharp-pointed.
Transverse section of leaf blade, physiology. Leaf blades consisting of midrib (there being only a flange of lamina and two bundles on each side, these increasingly reduced acropetally). Lamina mid-zone in transverse section open.
C4; XyMS+. PCR sheaths of the primary vascular bundles interrupted; interrupted both abaxially and adaxially. PCR sheath extensions absent. PCR cell chloroplasts centripetal. Mesophyll without arm cells (although with some hints of wall intrusions in the material seen). Midrib having a conventional arc of bundles (a large arc of about 16 bundles, with the median slightly larger than the rest); with colourless mesophyll adaxially (the entire adaxial area of the leaf being colourless). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present (with the large lamina-flange bundles only); forming figures (the lamina-flange bundles only). Sclerenchyma all associated with vascular bundles. The lamina margins with fibres.
Classification. Watson & Dallwitz (1994): Chloridoideae; main chloridoid assemblage. Soreng et al. (2015): Chloridoideae; Cynodonteae; Eleusininae. 1 species (R. altera (Rendle) Chiov.).
Distribution, phytogeography, ecology. Eastern tropical and southern Africa.
Mesophytic; species of open habitats; glycophytic. Shallow soils in grasslands.
References, etc. Leaf anatomical: this project.
Illustrations. • General aspect (R. altera): Gibbs Russell et al., 1990. • R. altera, abaxial epidermis of leaf blade: this project. • R. altera, TS leaf blade: this project
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’.