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The grass genera of the world

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

Ophiuros Gaertn. f.

Habit, vegetative morphology. Annual, or perennial; caespitose (forming tall clumps). Culms 100–250 cm high; branched above. The branching simple. Culms tuberous, or not tuberous. Culm nodes glabrous. Culm internodes solid. Leaves not basally aggregated; non-auriculate. Leaf blades broad, or narrow; flat, or folded, or rolled (convolute); without cross venation; persistent. Ligule a fringed membrane.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets all alike in sexuality (ostensibly), or of sexually distinct forms on the same plant (if the vestigial pedicellate members are perceived as such); hermaphrodite, or hermaphrodite and sterile; overtly heteromorphic (if the pedicellate members are perceived as spikelets).

Inflorescence. Inflorescence compound paniculate (with slender, cylindrical, distichous spikes, terminal on culm branches). Rachides hollowed. Inflorescence spatheate; a complex of ‘partial inflorescences’ and intervening foliar organs. Spikelet-bearing axes spikelike (the spikelets sunk in hollows of the terete rachis); solitary, or clustered (fascicled); with substantial rachides; disarticulating; disarticulating at the joints. ‘Articles’ non-linear; with a basal callus-knob; disarticulating transversely; glabrous. Spikelets solitary (ostensibly solitary), or paired (acknowledging an ‘adnate pedicel’); not secund (the sessile spikelets in two opposite rows); distichous; sessile and pedicellate; consistently in ‘long-and-short’ combinations (disguisedly so); in pedicellate/sessile combinations. Pedicels of the ‘pedicellate’ spikelets discernible, but fused with the rachis. The ‘shorter’ spikelets hermaphrodite. The ‘longer’ spikelets sterile (and reduced to the adnate pedicel).

Female-sterile spikelets. The pedicelled spikelet absent, being represented only by its pedicel, which is fused to the internode and sometimes barely recognisable.

Female-fertile spikelets. Spikelets abaxial; compressed dorsiventrally; falling with the glumes (and with the joint). Rachilla terminated by a female-fertile floret. Hairy callus absent.

Glumes two; more or less equal; long relative to the adjacent lemmas; awnless; very dissimilar (the lower thickly leathery or crustaceous, the upper thinly hyaline). Lower glume not two-keeled (with or without narrow wings at the tip); convex on the back to flattened on the back; not pitted; lacunose with deep depressions, or rugose (with a basal transverse groove); 5–7 nerved. Upper glume 3 nerved. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. The proximal incomplete florets 1; paleate; male, or sterile. The proximal lemmas awnless; 0 nerved, or 2 nerved; not becoming indurated.

Female-fertile florets 1. Lemmas less firm than the glumes (thinly membranous); not becoming indurated; awnless; hairless; non-carinate; 0 nerved, or 2 nerved, or 3 nerved. Palea present; entire; not indurated (thin); 2-nerved. Lodicules present; 2; free; fleshy; glabrous. Stamens 3. Anthers not penicillate. Ovary apically glabrous. Styles free to their bases. Stigmas 2.

Fruit, embryo and seedling. Fruit slightly compressed dorsiventrally. Embryo small (about 1/4 of the fruit length).

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells similar in shape costally and intercostally; of similar wall thickness costally and intercostally. Mid-intercostal long-cells rectangular (with rounded corners), or fusiform (or tending to this); having markedly sinuous walls. Microhairs present; panicoid-type; (51–)52.5–54(–58.5) microns long; 10.5–12 microns wide at the septum. Microhair total length/width at septum 4.25–5.6. Microhair apical cells 24–40.5 microns long. Microhair apical cell/total length ratio 0.69–0.74. Stomata common; 24–29 microns long. Subsidiaries triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs; silicified. Costal short-cells predominantly paired. Costal silica bodies ‘panicoid-type’; mainly cross shaped; not sharp-pointed.

Transverse section of leaf blade, physiology. C4; XyMS–. Mesophyll with radiate chlorenchyma. Leaf blade adaxially flat. Midrib conspicuous; having a conventional arc of bundles; with colourless mesophyll adaxially. Bulliforms present in discrete, regular adaxial groups (in the large-celled epidermis); in simple fans (the groups large celled, Zea-type). Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders present; forming ‘figures’. Sclerenchyma all associated with vascular bundles.

Phytochemistry. Leaves without flavonoid sulphates (1 species).

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

Distribution, phytogeography, ecology. 1 in northeast tropical Africa, 6 in the Indomalayan region, Australia.

Damp places in savanna.

Rusts and smuts. Smuts from Ustilaginaceae. Ustilaginaceae — Sphacelotheca and Ustilago.

References, etc. Leaf anatomical: studied by us - O. megaphyllus Stapf ex Haines.

Special comments. Fruit data wanting. Illustrations. • O. exaltatus: Gardner, 1952. • O. exaltatus, as Rottboellia: Rose Innes, Ghana Grasses (1977). • Inflorescence detail of O. exaltatus: this project. • Disarticulated inflorescence ‘joint’ of R. exaltata: this project. Ophiuros exaltatus. Sessile spikelet (left), pedicellate spikelet with its pedicel fused with the rachis (right), and basal elaiosome. • O. exaltatus, 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: 11th December 2017.’.