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The grass genera of the world

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

Humbertochloa A. Camus & Stapf

Habit, vegetative morphology. Perennial. The flowering culms leafy. Culms about 20–100 cm high; woody and persistent (slender, bamboo-like); branched above. Culm internodes hollow. Plants unarmed. Leaves not basally aggregated; non-auriculate; without auricular setae. Leaf blades broad; 10–30 mm wide (and 2–9 cm long); conspicuously cordate; pseudopetiolate; cross veined; disarticulating from the sheaths; rolled in bud. Ligule present; truncate (short).

Reproductive organization. Plants monoecious with all the fertile spikelets unisexual; without hermaphrodite florets. The spikelets of sexually distinct forms on the same plant; female-only and male-only (separate male and female spikelets in the conspicuous terminal inflorescences, and sometimes with small, few-spikeleted female inflorescences in the upper leaf sheaths). The male and female-fertile spikelets in different inflorescences. The spikelets overtly heteromorphic (the males much smaller). Plants with hidden cleistogenes, or without hidden cleistogenes. The hidden cleistogenes (when present) in the leaf sheaths (in the form of few-spikeleted female inflorescences, in the upper leaf sheaths).

Inflorescence. Inflorescence with the spikelets in secondary, short spiciform subsessile ‘racemes’, the latter borne alternately along the thickened midrib on one side of the thickened, leaf-like primary axis. Rachides flattened and winged (spathiform). Inflorescence spatheate. Spikelet-bearing axes very much reduced (the female racemes with one spikelet, the males with 1–4); disarticulating. Spikelets with ‘involucres’ of ‘bristles’ (the glumes of vestigial spikelets?). The ‘bristles’ persisting on the axis. Spikelets secund (i.e., on one side of the main axis).

Female-sterile spikelets. Male spikelets borne 1–4 per raceme, smaller than the females, the upper (fertile) floret with 3–6 stamens and a vestigial ovary. Male florets 3–6 staminate.

Female-fertile spikelets. Spikelets 10–11 mm long; oblong; abaxial; compressed laterally (asymmetric); falling with the glumes. Rachilla prolonged beyond the uppermost female-fertile floret. Hairy callus absent.

Glumes two; very unequal; shorter than the adjacent lemmas; very dissimilar (G1 shorter, rigid and subulate, G2 membranous, keeled, folded, lanceolate or ovate-oblong). Lower glume 0 nerved. Upper glume 5–7 nerved. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. The proximal incomplete florets 1; sterile. The proximal lemmas awnless; rigid, thick.

Female-fertile florets 1. Lemmas lanceolate-acuminate; thinly leathery; entire; pointed; awnless; hairless; non-carinate (dorsally rounded); 7–11 nerved (the nerves anastomosing above). Palea present; conspicuous but relatively short (about two-thirds the lemma length); entire (lanceolate); awnless, without apical setae; not indurated (thinly leathery); 2-nerved. Lodicules present; 2; membranous (‘hyaline’); heavily vascularized. Stamens 0, or 3–6 (staminodal). Ovary apically glabrous. Styles fused (into one long style). Stigmas 2.

Fruit, embryo and seedling. Fruit free from both lemma and palea. Hilum long-linear. Embryo small. Endosperm containing compound starch grains.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells markedly different in shape costally and intercostally (the costals narrower); of similar wall thickness costally and intercostally (fairly thin walled). Mid-intercostal long-cells rectangular; having markedly sinuous walls (the sinuosity coarse). Microhairs present; elongated; clearly two-celled; panicoid-type; 57–69 microns long; 7.5–9 microns wide at the septum. Microhair total length/width at septum 6.3–9.2. Microhair apical cells 30–37.5 microns long. Microhair apical cell/total length ratio 0.5–0.57. Stomata common; 24–27 microns long. Subsidiaries mostly triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs (these abundant, small); silicified. Intercostal silica bodies crescentic, or tall-and-narrow, or oryzoid-type (small). A few bulbous-based prickles present. Crown cells absent. Costal short-cells neither distinctly grouped into long rows nor predominantly paired (seemingly nearly all solitary). Costal silica bodies saddle shaped, or oryzoid (predominating, intergrading with the saddles).

Transverse section of leaf blade, physiology. C3 (the bundles very widely separated); XyMS+ (the mestome sheath itself double in the midrib bundle). Mesophyll with non-radiate chlorenchyma; probably with adaxial palisade (judging from the distorted material seen); with arm cells; without fusoids. Leaf blade ‘nodular’ in section. Midrib conspicuous (by virtue of its large bundle and small, blunt, abaxial keel); with one bundle only. The lamina symmetrical on either side of the midrib. Bulliforms present in discrete, regular adaxial groups (these large and wide); in simple fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; forming ‘figures’ (the median with a large, pronounced I, the other bundles with slight ‘anchors’ or I’s). Sclerenchyma all associated with vascular bundles.

Special diagnostic feature. Spikelets borne on one side of a broad, leaflike rachis.

Classification. Watson & Dallwitz (1994): Bambusoideae; Oryzodae; Phyllorhachideae. Soreng et al. (2015): Oryzoideae; Phyllorachideae. 2 species.

Distribution, phytogeography, ecology. Tropical East Africa, Madagascar.

Shade species. In forests.

References, etc. Morphological/taxonomic: Hubbard 1939. Leaf anatomical: studied by us - H. greenwayi C.E. Hubbard.

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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.’.