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. Upper culm leaf blades fully developed. 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, 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. 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); spikelet-bearing axes 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. Spikelets with proximal incomplete 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 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.
Taxonomy. Panicoideae; Andropogonodae; Andropogoneae; Rottboelliinae.
Distribution, ecology, phytogeography. 1 species; tropical Africa and Asia. Hydrophytic, or helophytic; species of open habitats; glycophytic. Swamps and river margins.
Paleotropical. African and Indomalesian. Sudano-Angolan, West African Rainforest, and Namib-Karoo. Indian and Indo-Chinese. Sahelo-Sudanian, Somalo-Ethiopian, South Tropical African, and Kalaharian.
References, etc. Leaf anatomical: this project, and photos provided by R.P. Ellis.
Special comments. Fruit data wanting.
Illustrations. • General morphology. • Abaxial epidermis of leaf blade
Cite this publication as: Watson, L., and Dallwitz, M. J. (1992 onwards). ‘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.’ http://biodiversity.uno.edu/delta/. Version: 18th August 1999. Dallwitz (1980), Dallwitz, Paine and Zurcher (1993 onwards, 1998), and Watson and Dallwitz (1994), and Watson, Dallwitz, and Johnston (1986) should also be cited (see References).
