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The grass genera of the world

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

Oryzidium C.E. Hubb. & Schweick.

Habit, vegetative morphology. Floating perennial; stoloniferous. Culms 40–120 cm high (the lower internodes trailing in water or floating); herbaceous (spongy); branched above. Culm nodes glabrous. Culm leaf sheaths persisting even when permanently submerged. Culm internodes solid (spongy). Plants unarmed. Young shoots intravaginal. Leaves not basally aggregated; non-auriculate. Leaf blades linear; narrow; 6–10 mm wide; flat; without cross venation; persistent. Ligule a fringe of hairs; 3–4 mm long. Contra-ligule absent.

Reproductive organization. Plants bisexual, all with bisexual spikelets; without hermaphrodite florets (the lower floret male, the upper female).

Inflorescence. Inflorescence paniculate; narrow, the branches nearly erect; espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets solitary; not secund; pedicellate; somewhat imbricate.

Female-fertile spikelets. Spikelets 8–10 mm long; lanceolate; compressed dorsiventrally; biconvex; falling with the glumes; not disarticulating between the florets; with distinctly elongated rachilla internodes between the florets (i.e., the upper floret stipitate). Rachilla terminated by a female-fertile floret; hairless. Hairy callus absent.

Glumes two; very unequal; (the upper) long relative to the adjacent lemmas; hairless; glabrous (G1), or scabrous (G2, on the veins); (the upper) awned (attenuate into a long straight awn); non-carinate; very dissimilar (the G1 a small, membranous, truncate scale, the G2 large, firm, awned). Lower glume shorter than the lowest lemma; 0 nerved, or 3 nerved (faint). Upper glume 5–7 nerved. 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; not becoming conspicuously hardened and enlarged laterally. The proximal incomplete florets male (with 3 stamens). The proximal lemmas acuminate; awned (attenuate); 5 nerved; decidedly exceeding the female-fertile lemmas; similar in texture to the female-fertile lemmas; not becoming indurated.

Female-fertile florets 1. Lemmas similar in texture to the glumes to decidedly firmer than the glumes (thinly leathery); smooth; not becoming indurated; entire; pointed; mucronate (or mucronulate); hairless; non-carinate; having the margins lying flat on the palea; with a clear germination flap; 7 nerved. Palea present; relatively long; tightly clasped by the lemma; entire; awnless, without apical setae; textured like the lemma; not indurated; 2-nerved; keel-less. Lodicules present; 2; free; fleshy; glabrous; not or scarcely vascularized. Stamens 0 (the male floret with non-penicillate anthers 2.5–3 mm long). Ovary apically glabrous. Styles free to their bases. Stigmas 2; white.

Fruit, embryo and seedling. Fruit free from both lemma and palea (but clasped below by the flaps of the palea); small (3–3.5 mm long); ellipsoid; compressed dorsiventrally. Hilum short. Embryo large; not waisted.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; panicoid-type; (72–)75–84(–90) microns long; (4.8–)5.7–6 microns wide at the septum. Microhair total length/width at septum 12–18.8. Microhair apical cells (46–)51–56(–57) microns long. Microhair apical cell/total length ratio 0.63–0.68. Stomata common (easy to find, but thinly spread); 27–33 microns long. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs. Costal short-cells conspicuously in long rows (some veins), or predominantly paired (some veins), or neither distinctly grouped into long rows nor predominantly paired (some veins). Costal silica bodies ‘panicoid-type’; all very small, dumb-bell shaped and nodular; not sharp-pointed.

Transverse section of leaf blade, physiology. C4; XyMS+. PCR sheath outlines even. PCR cell chloroplasts seemingly centripetal. Leaf blade with distinct, prominent adaxial ribs; with the ribs more or less constant in size. Midrib conspicuous (with a large air-space on either side of the large bundle); having a conventional arc of bundles (one large bundle, two small); with colourless mesophyll adaxially. Bulliforms present in discrete, regular adaxial groups; in simple fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders absent. Sclerenchyma all associated with vascular bundles.

Classification. Watson & Dallwitz (1994): Panicoideae; Panicodae; Paniceae. Soreng et al. (2015): Panicoideae; Panicodae; Paniceae. 1 species (O. barnardii).

Distribution, phytogeography, ecology. Southern tropical Africa.

Hydrophytic (in permanent water); species of open habitats; glycophytic.

References, etc. Morphological/taxonomic: Hubbard and Schweickerdt 1936. Leaf anatomical: studied by us, and photos of O. barnardii provided by R.P. Ellis.

Illustrations. • General aspect (O. barnardii): Gibbs Russell et al., 1990. • Lemma and palea close-up of O. barnardii: this project. Oryzidium barnardii. Leathery fertile lemma with margins lying flat and exposed on the similarly textured palea. • O. barnardii, leaf blade TS: this project. • O. barnardii, T.S. of leaf blade midrib region with lacunae: 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: 11th December 2017.’.