Ophiuros Gaertn. f.
Habit, vegetative morphology. Annual, or perennial; caespitose (forming tall clumps). Culms 100–250 cm high; branched above; 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; a fringed membrane.
Reproductive organization. Plants bisexual, 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. Spikelets with proximal incomplete 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 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).
Taxonomy. Panicoideae; Andropogonodae; Andropogoneae; Rottboelliinae.
Distribution, ecology, phytogeography. 4 species; 1 in northeast tropical Africa, 6 in the Indomalayan region, Australia. Damp places in savanna.
Paleotropical and Australian. African and Indomalesian. Saharo-Sindian and Sudano-Angolan. Indian, Indo-Chinese, Malesian, and Papuan. North and East Australian. Somalo-Ethiopian. Tropical North and East Australian.
Rusts and smuts. Smuts from Ustilaginaceae. Ustilaginaceae — Sphacelotheca and Ustilago.
References, etc. Leaf anatomical: this project.
Special comments. Fruit data wanting.
Illustrations. • General aspect, inflorescence
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).
