| # The grass genera of the world |

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

### Vossia Wall. & Griff.

Habit, vegetative morphology. Aquatic perennial; rhizomatous. The flowering culms leafy. Culms 100–200 cm high (above the water, from floating culms up to 7 m long); herbaceous (propagating from stem fragments); to 1 cm in diameter. Culm leaves present. Culm internodes solid. Leaves not basally aggregated; non-auriculate. Leaf blades linear to linear-lanceolate; broad; 6–25 mm wide (up to 1 m long); flat; without cross venation. Ligule present; a fringed membrane.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets of sexually distinct forms on the same plant, or all alike in sexuality; hermaphrodite, or hermaphrodite and male-only; homomorphic; all in heterogamous combinations.

Inflorescence. Inflorescence of spicate main branches (rarely a single ‘raceme’); usually digitate. Primary inflorescence branches several to many, rarely only one. Rachides hollowed. Spikelets all partially embedded in the rachis. Inflorescence espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes ‘racemes’ (spiciform, subcylindrical or flattened, with 12 or more internodes); the spikelet-bearing axes with more than 10 spikelet-bearing ‘articles’ (12 or more); clustered; with substantial rachides; disarticulating (but rachis not very fragile); disarticulating at the joints. ‘Articles’ non-linear (flattened dorsally, inflated above); not appendaged; disarticulating transversely; glabrous. Spikelets paired; not secund; distichous (in alternating pairs on the zigzag rachis); 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 hermaphrodite, or male-only.

Female-fertile spikelets. Spikelets 6–8 mm long; compressed dorsiventrally; planoconvex; falling with the glumes (and with the adjacent joint and pedicel). Rachilla terminated by a female-fertile floret. Hairy callus absent.

Glumes two; more or less equal (when the apical convergence of the veins is considered, but the very long awn of the lower confuses the issue); (the longer) long relative to the adjacent lemmas; hairless (scabrid on margins and keels); pointed; awned (or at least, the G1 long-caudate, with a flat tail); carinate (G2), or non-carinate (G1); very dissimilar (the G1 leathery, flat-backed, caudate-acuminate and 2-keeled, the G2 thinner and naviculate). Lower glume two-keeled; flattened on the back; not pitted; relatively smooth; indistinctly many veined between the keels. Upper glume indistinctly several to many veined. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. The proximal incomplete florets 1; paleate. Palea of the proximal incomplete florets fully developed. The proximal incomplete florets male. The proximal lemmas awnless; 2 nerved; more or less equalling 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 (hyaline); not becoming indurated; entire; pointed; awnless; hairless; glabrous; non-carinate; without a germination flap; 3 nerved. Palea present; relatively long; tightly clasped by the lemma; entire; awnless, without apical setae; textured like the lemma; not indurated; 2-nerved; 2-keeled. Lodicules present; 2; free; fleshy; glabrous. Stamens 3. Anthers not penicillate; without an apically prolonged connective. Ovary apically glabrous. Stigmas 2.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous (in places). Papillae present (in places), or absent; where detected, intercostal. Intercostal papillae consisting of one oblique swelling per cell (where seen, at one end of the long-cells). Long-cells similar in shape costally and intercostally; of similar wall thickness costally and intercostally (of medium thickness). Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; elongated; clearly two-celled; panicoid-type. Stomata common. Subsidiaries non-papillate; dome-shaped to triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; obscurely in cork/silica-cell pairs; silicified. Intercostal silica bodies tall-and-narrow (abundant, but small and seemingly poorly developed). With rows of large prickles on some of the costae. Costal short-cells predominantly paired. Costal silica bodies present and well developed to poorly developed; mostly tall-and-narrow (abundant, but mostly small and seemingly poorly developed).

Transverse section of leaf blade, physiology. C4; XyMS–. PCR sheath outlines uneven. PCR cell chloroplasts centrifugal/peripheral. Mesophyll with radiate chlorenchyma. Leaf blade with distinct, prominent adaxial ribs to ‘nodular’ in section; with the ribs very irregular in sizes (emphatically so). Midrib very conspicuous; having a conventional arc of bundles (with a large median primary, a large primary bordering the midrib on each side, and small bundles in between); with colourless mesophyll adaxially (and an adaxial lignified hypodermal layer). The lamina distinctly asymmetrical on either side of the midrib. Bulliforms present in discrete, regular adaxial groups; in simple fans (these large, Zea-type, often situated over a minor bundle). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present (with the main bundles); sometimes forming ‘figures’ (slight I’s only). Sclerenchyma all associated with vascular bundles.

Cytology. 2n = 20.

Classification. Watson & Dallwitz (1994): Panicoideae; Andropogonodae; Andropogoneae; Rottboelliinae. Soreng et al. (2015): Panicoideae; Andropogonodae; Andropogoneae; Rottboelliinae. 1 species (V. cuspidata).

Distribution, phytogeography, ecology. Tropical Africa and Asia.

Hydrophytic, or helophytic; species of open habitats; glycophytic. Swamps and river margins.

References, etc. Leaf anatomical: studied by us, and photos provided by R.P. Ellis.

Special comments. Fruit data wanting.

Illustrations. • Vossia cuspidata: Jacques-Félix, 1962. • General morphology (V. cuspidata): Gibbs Russell et al., 1990. • Vossia cuspidata, abaxial epidermis of leaf blade: 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: 15th June 2025. delta-intkey.com’.

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