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The grass genera of the world

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

Monocymbium Stapf

Name referring to solitary racemes.

Habit, vegetative morphology. Perennial; caespitose. Culms 30–120 cm high; herbaceous; branched above, or unbranched above. Leaves not basally aggregated; non-auriculate. Leaf blades linear; narrow; flat (tapering to a sharp point); without cross venation. Ligule an unfringed membrane; truncate.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets of sexually distinct forms on the same plant; hermaphrodite and male-only; overtly heteromorphic (the pedicellate spikelets awnless); all in heterogamous combinations.

Inflorescence. Inflorescence paniculate (of solitary ‘racemes’, loosely gathered into a false panicle); with capillary branchlets; conspicuously spatheate (each raceme embraced by a reddish spatheole); a complex of ‘partial inflorescences’ and intervening foliar organs. Spikelet-bearing axes dense ‘racemes’ (the spikelets more or less concealing the short internodes); the spikelet-bearing axes with 6–10 spikelet-bearing ‘articles’, or with more than 10 spikelet-bearing ‘articles’ (with at least 6 spikelet pairs); solitary; with very slender rachides (filiform); disarticulating; disarticulating at the joints. ‘Articles’ linear; not appendaged; disarticulating obliquely; densely long-hairy. Spikelets paired; secund; sessile and pedicellate; consistently in ‘long-and-short’ combinations; in pedicellate/sessile combinations. Pedicels of the ‘pedicellate’ spikelets free of the rachis. The ‘shorter’ spikelets hermaphrodite. The ‘longer’ spikelets male-only.

Female-sterile spikelets. Pedicellate spikelets male, similar in form to the sessile members but awnless, with a linear callus. The lemmas awnless.

Female-fertile spikelets. Spikelets compressed dorsiventrally (flattened dorsally, the sides rounded); falling with the glumes (deciduous with the adjacent joint and pedicel). Rachilla terminated by a female-fertile floret. Callus short (but not clearly distinct from G1, obscurely bearded); blunt.

Glumes two; more or less equal; long relative to the adjacent lemmas (exceeding them); hairy, or hairless; without conspicuous tufts or rows of hairs; (the upper) awned (from a notch); very dissimilar (thinly cartilaginous, only the G2 awned). Lower glume not two-keeled (naviculate, laterally compressed and keeled over its upper third); convex on the back; not pitted; relatively smooth; 7 nerved (?). Upper glume 3 nerved. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. Spikelets with proximal incomplete florets. The proximal incomplete florets 1; epaleate; sterile. The proximal lemmas awnless; more or less equalling the female-fertile lemmas to decidedly exceeding the female-fertile lemmas; similar in texture to the female-fertile lemmas (hyaline); not becoming indurated.

Female-fertile florets 1. Lemmas less firm than the glumes (except for the cartilaginous median zone); not becoming indurated; incised; 2 lobed; deeply cleft; awned. Awns 1; median; from a sinus; geniculate; hairless; much longer than the body of the lemma. Lemmas hairless; non-carinate; without a germination flap; 1 nerved. Palea absent. Lodicules present; 2; free; fleshy; glabrous. Stamens 3. Ovary apically glabrous. Styles free to their bases. Stigmas 2.

Fruit, embryo and seedling. Fruit compressed dorsiventrally. Hilum short. Embryo large.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells differing markedly in wall thickness costally and intercostally (costals thinner). Mid-intercostal long-cells rectangular; having markedly sinuous walls (mostly). Microhairs present; panicoid-type; 39–51 microns long; 5.4–6 microns wide at the septum. Microhair total length/width at septum 6.5–8.5. Microhair apical cells 21–26 microns long. Microhair apical cell/total length ratio 0.44–0.54. Stomata common; 27–30 microns long. Subsidiaries dome-shaped (mostly), or triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs (and solitary); silicified (but rarely so). Costal short-cells conspicuously in long rows. Costal silica bodies ‘panicoid-type’; cross shaped, butterfly shaped, and dumb-bell shaped; not sharp-pointed.

Transverse section of leaf blade, physiology. C4; XyMS–. PCR cell chloroplasts centrifugal/peripheral. Mesophyll with radiate chlorenchyma; traversed by columns of colourless mesophyll cells (a few of the arches reaching the abaxial epidermis, near midrib). Leaf blade adaxially flat. Midrib conspicuous (via a larger bundle and abaxial rib); with one bundle only. The lamina symmetrical on either side of the midrib. Bulliforms not present in discrete, regular adaxial groups (the epidermis mainly bulliform); associating with colourless mesophyll cells to form arches over small vascular bundles (especially near the midrib, in M. ceresiiforme). Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders present. Sclerenchyma all associated with vascular bundles.

Cytology. Chromosome base number, x = 5, or 10. 2n = 20. 2 ploid, or 4 ploid.

Classification. Watson & Dallwitz (1994): Panicoideae; Andropogonodae; Andropogoneae; Andropogoninae. Soreng et al. (2015): Panicoideae; Andropogonodae; Andropogoneae. 4 species.

Distribution, phytogeography, ecology. Tropical and southern Africa.

Mesophytic; species of open habitats; glycophytic. Savanna.

Economic aspects. Significant weed species: M. ceresiiforme.

Rusts and smuts. Rusts — Puccinia. Taxonomically wide-ranging species: Puccinia versicolor and ‘Uromycesclignyi. Smuts from Ustilaginaceae. Ustilaginaceae — Sphacelotheca.

References, etc. Leaf anatomical: studied by us - M. ceresiiforme (Nees) Stapf.

Illustrations. • M. lanceolatum: Jacques-Félix, 1962. • M. ceresiiforme: Hook. Ic. Pl. 19 (1889). • M. ceresiiforme, as Andropogon: Wood, Natal Plants 2 (1904). • General aspect (M. ceresiiforme): Gibbs Russell et al., 1990. • M. ceresiiforme, abaxial epidermis of leaf blade: this project

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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.’.