The grass genera of the world
Habit, vegetative morphology. Annual (with filiform culms); caespitose (or with solitary culms). Culms 7–18 cm high. Plants unarmed. Leaves not basally aggregated. Leaf blades linear; narrow; to 1.5 mm wide (1–6.5 cm long); flat, or rolled (involute); exhibiting multicellular glands abaxially (at the base of hairs). The abaxial leaf blade glands intercostal. Leaf blades without cross venation; persistent. Ligule a fringe of hairs; 1 mm long (with longer lateral tufts). Contra-ligule absent.
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets.
Inflorescence. Inflorescence of spicate main branches; contracted (to 7 cm long, with few-to-many 5–12 mm long incurved racemes); non-digitate. Primary inflorescence branches 3–11 (rarely 1–2). Inflorescence axes not ending in spikelets (the main axis and the lateral racemes ending in a naked scaberulous bristle). Inflorescence espatheate; not comprising partial inflorescences and foliar organs. Spikelet-bearing axes racemes; persistent. Spikelets solitary (alternate, contiguous); secund; biseriate; pedicellate (the pedicels short, bristly).
Female-fertile spikelets. Spikelets 1.6–2 mm long; compressed laterally; disarticulating above the glumes; disarticulating between the florets. Rachilla prolonged beyond the uppermost female-fertile floret; the rachilla extension with incomplete florets. Hairy callus not recorded: the callus referred to in the original description is the pedicel, beneath the persistent glumes.
Glumes two; very unequal; (the upper) long relative to the adjacent lemmas (equalling or exceeding the spikelets); hairy (with spreading tubercle-based hairs on the keel, fewer of them on G1); pointed (acutely acuminate); awned (aristate, aristate-acuminate or caudate-acuminate), or awnless (acutely acuminate); carinate (somewhat); similar (deciduous, lanceolate to narrowly ovate and acutely acuminate, membranous). Lower glume shorter than the lowest lemma to about equalling the lowest lemma; 1 nerved. Upper glume 1 nerved. Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets. The distal incomplete florets merely underdeveloped.
Female-fertile florets 6–12. Lemmas similar in texture to the glumes to decidedly firmer than the glumes (membranous to hyaline); not becoming indurated; entire, or incised; not deeply cleft (entire or shallowly emarginate); awnless to mucronate (apiculate or shortly mucronate); hairy (ciliate, with stiff, white hairs on the margins); carinate to non-carinate; 1 nerved. Palea present; relatively long; entire (truncate, oblong); awnless, without apical setae; 2-nerved; 2-keeled (but convex and gibbous below between the rigid keels). Palea keels hairy (pectinate-ciliate). Lodicules present (minute), or absent; when present, 2; glabrous. Stamens 2 (anthers 0.25–0.4 mm long, broadly oblong). Anthers 0.25–0.3 mm long; not penicillate; without an apically prolonged connective. Ovary apically glabrous. Styles free to their bases (slender). Stigmas 2.
Fruit, embryo and seedling. Fruit free from both lemma and palea; small (0.3–0.4 mm long); ellipsoid; not noticeably compressed (terete). Hilum short. Pericarp free. Embryo large; waisted.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells similar in shape costally and intercostally; of similar wall thickness costally and intercostally (the walls rather thick). Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; elongated; clearly two-celled; chloridoid-type. Microhair apical cell wall thinner than that of the basal cell but not tending to collapse. Microhairs (27–)31–32(–33) microns long. Microhair basal cells 12 microns long. Microhairs (6–)6.6–7.8(–9) microns wide at the septum. Microhair total length/width at septum 3.7–5.3. Microhair apical cells 18–19.5–21 microns long. Microhair apical cell/total length ratio 0.59–0.64. Stomata common; 18–27 microns long. Subsidiaries dome-shaped and triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; not paired (mostly solitary); silicified. Intercostal silica bodies absent. Costal short-cells predominantly paired, or neither distinctly grouped into long rows nor predominantly paired (paired, solitary and in short rows). Costal silica bodies present in alternate cell files of the costal zones; saddle shaped (predominating, a rather irregular small version), or tall-and-narrow to crescentic (few); 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 interrupted; interrupted abaxially only. PCR sheath extensions absent. PCR cell chloroplasts centrifugal/peripheral. Leaf blade with distinct, prominent adaxial ribs; with the ribs very irregular in sizes (there being a big, flat-topped rib towards each margin). Midrib conspicuous (via its large, round-topped adaxial rib and large bundle); with one bundle only. Bulliforms present in discrete, regular adaxial groups (and sometimes in irregular groups); sometimes in simple fans, or associated with colourless mesophyll cells to form deeply-penetrating fans (?). Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders present; forming figures (primary bundles). Sclerenchyma all associated with vascular bundles.
Classification. Watson & Dallwitz (1994): Chloridoideae; main chloridoid assemblage. Soreng et al. (2015): Chloridoideae; Eragrostideae; Eragrostidinae. 1 species (R. eruciformis).
Distribution, phytogeography, ecology. Southeast tropical Africa.
Mesophytic, or xerophytic; species of open habitats; glycophytic. Dry sandy places.
References, etc. Morphological/taxonomic: Elffers and Kennedy-OByrne 1949. Leaf anatomical: Metcalfe 1960; 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’.