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The grass genera of the world

L. Watson, T.D. Macfarlane, and M.J. Dallwitz

Rheochloa Filg., P.M. Peterson & Y. Herrera

Alluding to the flightless bird, Rhea, after which the type locality of the genus is named.

Type species: R. scabriflora Filg., P.M. Peterson & Y. Herrera.

Habit, vegetative morphology. Perennial; more or less decumbent (with flexuous culms). Culms 60–75 cm long; herbaceous; scandent to not scandent; decumbent, or decumbent; unbranched above (but occasionally branched basally); 15–18 noded. Culm nodes exposed; glabrous. Culm leaves present. Culm internodes hollow. Leaves not basally aggregated; non-auriculate. Sheaths rounded on the back, glabrous. Leaf blades lanceolate to ovate; narrow; 4–5 mm wide; flat, or rolled; without abaxial multicellular glands; without cross venation; persistent. Ligule a fringed membrane; truncate; 0.6–1 mm long. Contra-ligule absent.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets hermaphrodite.

Inflorescence. Inflorescence of spicate main branches (reddish); subdigitate. Primary inflorescence branches 3–5. Inflorescence with axes ending in spikelets. Rachides triangular in section. Inflorescence espatheate; not comprising ‘partial inflorescences’ and foliar organs. The racemes spikelet bearing to the base (more or less?). Spikelets solitary; secund; biseriate (?); subsessile to pedicellate (the pedicels 0.5–1 mm long); fairly distant from one another.

Female-fertile spikelets. Spikelets 5.4–5.6 mm long; red-purplish brown; strongly compressed laterally; disarticulating above the glumes; not disarticulating between the florets (?); with conventional internode spacings. Rachilla prolonged beyond the uppermost female-fertile floret (the prolongation well developed); hairless; the rachilla extension with incomplete florets (or rather, with one apical rudiment). Hairy callus absent. Callus short; blunt.

Glumes two (leathery); more or less equal; exceeding the spikelets; long relative to the adjacent lemmas; lateral to the rachis; hairless; finely scabrous along the midnerve; not pointed; not subulate; awnless (muticous); carinate; similar. Lower glume 1 nerved. Upper glume 1 nerved. Spikelets with female-fertile florets only, or with incomplete florets (usually, at least in the form of a terminal vestige). The incomplete florets distal to the female-fertile florets. The distal incomplete florets 1, or 2; merely underdeveloped; awnless. Spikelets without proximal incomplete florets.

Female-fertile florets 1 (the upper of the two well-developed florets then being male-only), or 2. Lemmas less firm than the glumes (hyaline); not becoming indurated; entire; awnless; hairless; glabrous to scabrous; carinate to non-carinate (?). The keel wingless. Lemmas without a germination flap; strongly 3 nerved; with the nerves non-confluent. Palea present; relatively long (almost equalling the lemma); apically notched; awnless, without apical setae; textured like the lemma (hyaline); not indurated; 2-nerved; 2-keeled. Palea back glabrous. Palea keels wingless; glabrous to scabrous. Lodicules present; 2; free; fleshy; glabrous; ‘heavily vascularised’. Stamens 3. Anthers 1–1.2 mm long; not penicillate; without an apically prolonged connective. Ovary apically glabrous. Styles free to their bases; free. Stigmas 2; ‘yellowish to tan’.

Fruit, embryo and seedling. Disseminule a free caryopsis. Fruit free from both lemma and palea; small (2.7–2.8 mm long); reddish brown; fusiform; not grooved; trigonous. Hilum short. Pericarp fused. Embryo large; not waisted.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present; costal, or costal and intercostal (? — most apparently costal, mainly in the form of two largish, oblique papillae per long-cell). Intercostal papillae not over-arching the stomata; several per cell (few – mostly two per long-cell). Long-cells similar in shape costally and intercostally (elongated-rectangular); of similar wall thickness costally and intercostally. Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; elongated; clearly two-celled; chloridoid-type. Microhair apical cell/total length ratio 0.3–0.7 (apical and basal cells more or less equal). Stomata common. Subsidiaries non-papillate; dome-shaped. Intercostal short-cells absent or very rare. Costal zones with short-cells. Costal short-cells predominantly paired, or neither distinctly grouped into long rows nor predominantly paired (the available drawing depicts them mostly (ostensibly?) solitary, with a few pairs. The intervening costal cells labelled there ‘sc’ are long-cells as interpreted conventionally and throughout the present data). Costal silica bodies present and well developed; present in alternate cell files of the costal zones; ‘panicoid-type’ (? — not adequately resolved in the available illustration).

Transverse section of leaf blade, physiology. Lamina mid-zone in transverse section open.

C4; XyMS+. PCR sheath outlines uneven. PCR sheaths of the primary vascular bundles interrupted; interrupted abaxially only. PCR sheath extensions absent. Mesophyll with radiate chlorenchyma. Leaf blade with distinct, prominent adaxial ribs to ‘nodular’ in section, or adaxially flat; with the ribs more or less constant in size (the adaxial ribs low and round-topped). Midrib seemingly not readily distinguishable (not mentioned in the available description); presumably with one bundle only; without colourless mesophyll adaxially. Bulliforms present in discrete, regular adaxial groups; in simple fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; forming ‘figures’. 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. scabriflora).

Distribution, phytogeography, ecology. Central Brazil.

Mesophytic (in humid grassland).

References, etc. Morphological/taxonomic: Filigueiras et al. (1999). Leaf anatomical: Filigueiras et al. (1999, text and drawings).

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.’.