The grass genera of the world
~ Melinis; cf. Tricholaena - Fosberg and Sachet 1981
Type species: Type: R. repens (Willd.) C.E.Hubb.
Including Monachyron Parl.
Habit, vegetative morphology. Annual (rarely), or perennial; rhizomatous, or stoloniferous, or caespitose, or decumbent. Culms 20–120 cm high; herbaceous; branched above, or unbranched above. Culm nodes hairy. Culm leaf sheaths rounded. Culm internodes hollow. Leaves not basally aggregated; auriculate (rarely), or non-auriculate. Leaf blades linear; broad (rarely), or narrow; flat, or rolled; not pseudopetiolate; without cross venation; persistent; rolled in bud. Ligule a fringed membrane to a fringe of hairs. Contra-ligule absent.
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets.
Inflorescence. Inflorescence paniculate, or of spicate main branches (often decompound, rarely composed of secund racemes); open, or contracted; with capillary branchlets, or without capillary branchlets. Primary inflorescence branches inserted all around the main axis. Inflorescence espatheate; not comprising partial inflorescences and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund; pedicellate. Pedicel apices discoid (often hairy).
Female-fertile spikelets. Spikelets 2–11 mm long; elliptic, or ovate; compressed laterally (often asymmetric); disarticulating above the glumes (the fruiting floret falling first), or falling with the glumes (falling from the pedicel); with conventional internode spacings, or with a distinctly elongated rachilla internode between the glumes. Rachilla terminated by a female-fertile floret. Hairy callus present, or absent.
Glumes two; very unequal; (the upper) long relative to the adjacent lemmas; hairy (G2 usually villous or pubescent below, rarely glabrous); awned (G2 only, sometimes awned or mucronate or beaked upwards), or awnless; very dissimilar (G1 a scale up to 1/3 spikelet length, or reduced to a vestige or rim, G2 longer, apically emarginate or bifid, and awned or mucronate from the sinus, firmly membranous or papery, curved on the back). Lower glume 0–1 nerved. Upper glume 5–7 nerved (often gibbous below). Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. Spikelets with proximal incomplete florets. The proximal incomplete florets 1; paleate, or epaleate (rarely). Palea of the proximal incomplete florets when present, fully developed to reduced. The proximal incomplete florets male, or sterile. The proximal lemmas awned; 5 nerved; decidedly exceeding the female-fertile lemmas (similar to the G2, or narrower and less gibbous); similar in texture to the female-fertile lemmas; not becoming indurated.
Female-fertile florets 1. Lemmas less firm than the glumes to similar in texture to the glumes (membranous to papery); smooth (shiny); not becoming indurated; white in fruit; entire (truncate), or incised (emarginate or minutely two-lobed); blunt; when incised, 2 lobed; not deeply cleft; awnless; hairless (usually glabrous, rarely ciliate); non-carinate; having the margins lying flat on the palea; without a germination flap; 5 nerved. Palea present; relatively long; apically notched; 2-nerved. Lodicules present; 2; free; fleshy; glabrous. Stamens 3. Anthers not penicillate. Ovary apically glabrous. Styles fused, or free to their bases. Stigmas 2; brown.
Fruit, embryo and seedling. Fruit free from both lemma and palea; small; ellipsoid; compressed laterally, or not noticeably compressed. Hilum short. Embryo large; waisted, or not waisted; without an epiblast; with a scutellar tail; with an elongated mesocotyl internode. Embryonic leaf margins overlapping.
Seedling with a long mesocotyl. First seedling leaf with a well-developed lamina. The lamina broad; curved; 18 veined.
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. Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; panicoid-type; 60–75–87 microns long; (4–)4.5–5.4(–6) microns wide at the septum. Microhair total length/width at septum 12–19.3. Microhair apical cells (35–)40–47(–48) microns long. Microhair apical cell/total length ratio 0.55–0.67. Stomata common; (27–)28.5–30(–36) microns long. Subsidiaries triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs and not paired (solitaries); silicified (when paired), or not silicified. Intercostal silica bodies cross-shaped. Costal short-cells conspicuously in long rows. Costal silica bodies panicoid-type; cross shaped to dumb-bell shaped, or nodular; not sharp-pointed.
Transverse section of leaf blade, physiology. C4; biochemical type PCK (R. repens); XyMS+. PCR sheath outlines uneven. PCR sheath extensions absent. PCR cell chloroplasts ovoid; with well developed grana; centrifugal/peripheral. Mesophyll with radiate chlorenchyma. Leaf blade adaxially flat. Midrib conspicuous, or not readily distinguishable; with one bundle only, or having a conventional arc of bundles (rarely); with colourless mesophyll adaxially, or without colourless mesophyll adaxially. Bulliforms present in discrete, regular adaxial groups; in simple fans and 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. Sclerenchyma all associated with vascular bundles.
Culm anatomy. Culm internode bundles in three or more rings.
Phytochemistry. Leaves without flavonoid sulphates (2 species). Leaf blade chlorophyll a:b ratio 3.63.
Cytology. Chromosome base number, x = 9. 2n = 36. 4 ploid.
Classification. Watson & Dallwitz (1994): Panicoideae; Panicodae; Paniceae (Melinideae). Soreng et al. (2015): Panicoideae; Panicodae; Paniceae; Melidininae. 14 species.
Distribution, phytogeography, ecology. Tropical Africa, Madagascar, Arabia to Indochina.
Commonly adventive. Species of open habitats; glycophytic. Savanna and grassland, often in disturbed ground.
Economic aspects. Significant weed species: R. repens.
Rusts and smuts. Rusts Puccinia. Taxonomically wide-ranging species: Puccinia levis. Smuts from Tilletiaceae. Tilletiaceae Entyloma.
References, etc. Leaf anatomical: Metcalfe 1960; studied by us - R. repens (Willd.) Hubbard.
Illustrations. • R. repens: Gardner, 1952. • General aspect (R. repens): Gibbs Russell et al., 1990. • R. repens, part of inflorescence in close-up: this project. • R. repens, abaxial epidermis of leaf blade: this project. • R. repens, fluorescence image TS imasge of leaf blade: original
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’.