Oplismenus P. Beauv.
From the Greek hoplismenos (armed), alluding to the awns.
Including Hekaterosachne Steud., Hippagrostis Kuntze, Orthopogon R. Br.
Habit, vegetative morphology. Annual, or perennial; decumbent. Culms 10–100 cm high; herbaceous; freely branched above. Culm nodes hairy. Culm internodes solid, or hollow. Leaves not basally aggregated; non-auriculate. Leaf blades linear to ovate; broad, or narrow; not setaceous; flat (thin); pseudopetiolate, or not pseudopetiolate; cross veined, or without cross venation; persistent; rolled in bud; a fringed membrane (very short), or a fringe of hairs.
Reproductive organization. Plants bisexual, with bisexual spikelets; with hermaphrodite florets.
Inflorescence. Inflorescence of spicate main branches (short unilateral racemes along a central axis); open. Primary inflorescence branches borne biseriately on one side of the main axis. Inflorescence espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets solitary, or paired (or the lower member reduced, or in clusters); secund; biseriate; shortly pedicellate; imbricate, or not imbricate; not in distinct ‘long-and-short’ combinations.
Female-fertile spikelets. Spikelets elliptic, or lanceolate, or ovate; abaxial; weakly compressed laterally, or not noticeably compressed to compressed dorsiventrally; falling with the glumes. Rachilla terminated by a female-fertile floret. Hairy callus present.
Glumes two; more or less equal; shorter than the adjacent lemmas, or long relative to the adjacent lemmas; dorsiventral to the rachis; not pointed; awned (both or at least the lower, the awn of the lower always longer); carinate; similar (herbaceous, the awns often viscid). Lower glume 3–5 nerved. Upper glume 5 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 to reduced. The proximal incomplete florets male, or sterile. The proximal lemmas shortly awned, or awnless; 5–9 nerved; not becoming indurated.
Female-fertile florets 1. Lemmas dorsally compressed; similar in texture to the glumes to decidedly firmer than the glumes (papery to leathery); smooth (glossy); becoming indurated to not becoming indurated; white in fruit, or yellow in fruit; entire; indistinctly crested at the tip, or not crested; awnless; hairless; carinate to non-carinate; having the margins inrolled against the palea; with a clear germination flap; 3–5 nerved. Palea present; relatively long; entire (acute); awnless, without apical setae; textured like the lemma (smooth, glossy); indurated, or not indurated; 2-nerved. Lodicules present; 2; fleshy. Stamens 3. Anthers 1–2 mm long; not penicillate. Ovary glabrous. Styles free to their bases. Stigmas 2.
Fruit, embryo and seedling. Fruit ellipsoid; longitudinally grooved (slightly), or not grooved; compressed dorsiventrally. Hilum short to long-linear (oblong, up to a half as long as the fruit). Embryo large. Endosperm hard; without lipid; containing only simple starch grains. Embryo without an epiblast; with a scutellar tail; with an elongated mesocotyl internode. Embryonic leaf margins overlapping.
Seedling with a long mesocotyl. First seedling leaf with a well-developed lamina. The lamina broad; supine; 13–20 veined.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells markedly different in shape costally and intercostally (the costals narrow-rectangular); of similar wall thickness costally and intercostally (thin walled). Intercostal zones exhibiting many atypical long-cells, or without typical long-cells (incorporating or comprising squarish long-cells). Mid-intercostal long-cells rectangular (usually short, some irregular in shape); having markedly sinuous walls. Microhairs present; panicoid-type; (38–)46–59(–60) microns long; 4.5–6 microns wide at the septum. Microhair total length/width at septum 10–11.3. Microhair apical cells (20–)25–34.5(–36) microns long. Microhair apical cell/total length ratio 0.52–0.55. Stomata absent or very rare, or common; (34–)36–39(–42) microns long. Subsidiaries low dome-shaped, or triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common, or absent or very rare; not paired (mainly solitary); silicified, or not silicified. Intercostal silica bodies when present, cross-shaped. Costal short-cells conspicuously in long rows. Costal silica bodies ‘panicoid-type’; cross shaped to dumb-bell shaped, or nodular; not sharp-pointed.
Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with radiate chlorenchyma; Isachne-type to not Isachne-type. Leaf blade with distinct, prominent adaxial ribs, or adaxially flat; with the ribs more or less constant in size. Midrib conspicuous; with one bundle only. Bulliforms present in discrete, regular adaxial groups (these wide); in simple fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; forming ‘figures’. Sclerenchyma all associated with vascular bundles.
Culm anatomy. Culm internode bundles in one or two rings.
Phytochemistry. Leaves without flavonoid sulphates (O. hirtellus).
Cytology. Chromosome base number, x = 9, 10, and 11. 2n = 18, 36, 54, 72, and 90. Chromosomes ‘snall’.
Taxonomy. Panicoideae; Panicodae; Paniceae.
Distribution, ecology, phytogeography. 7 species; tropical and subtropical. Mesophytic; shade species; glycophytic. In forest.
Holarctic, Paleotropical, Neotropical, Cape, Australian, and Antarctic. Boreal and Tethyan. African, Madagascan, Indomalesian, Polynesian, and Neocaledonian. Euro-Siberian, Eastern Asian, and Atlantic North American. Mediterranean and Irano-Turanian. Saharo-Sindian, Sudano-Angolan, West African Rainforest, and Namib-Karoo. Indian, Indo-Chinese, Malesian, and Papuan. Fijian. Caribbean, Venezuela and Surinam, Amazon, Central Brazilian, Pampas, and Andean. North and East Australian. New Zealand. European. Southern Atlantic North American and Central Grasslands. Sahelo-Sudanian, Somalo-Ethiopian, South Tropical African, and Kalaharian. Tropical North and East Australian and Temperate and South-Eastern Australian.
Rusts and smuts. Rusts — Phakopsora and Puccinia. Smuts from Tilletiaceae and from Ustilaginaceae. Tilletiaceae — Tilletia. Ustilaginaceae — Ustilago.
Economic importance. Significant weed species: O. burmanii, O. compositus, O. hirtellus, O. undulatifolius. Important native pasture species: O. compositus.
References, etc. Leaf anatomical: Metcalfe 1960; this project.
Illustrations. • General aspect. • Inflorescence. Oplismenus aemulus. • Inflorescence detail. Oplismenus aemulus. • 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).
