Oplismenopsis L. Parodi
From Oplismenus (another grass genus, q.v.) and the Greek opsis (appearance), denoting likeness.
Habit, vegetative morphology. Aquatic perennial; rhizomatous. Culms herbaceous; to 1.2 cm in diameter; branched above. Culm nodes glabrous. Culm internodes hollow. Leaves not basally aggregated; non-auriculate. Sheaths glabrous, with cross-veins. Leaf blades lanceolate to ovate; broad; 10–27 mm wide; cordate; flat, or rolled (convolute); shortly pseudopetiolate; without cross venation; persistent; a fringed membrane; truncate; 1–1.5 mm long. Contra-ligule absent.
Reproductive organization. Plants bisexual, with bisexual spikelets; with hermaphrodite florets.
Inflorescence. Inflorescence of spicate main branches, or paniculate (of loose, non-digitate racemes); open; espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets solitary; secund; biseriate; pedicellate.
Female-fertile spikelets. Spikelets about 9 mm long; lanceolate; adaxial; compressed dorsiventrally; falling with the glumes. Rachilla terminated by a female-fertile floret. Hairy callus absent.
Glumes two; very unequal; (the upper) about equalling the spikelets (the lower about 1/2–1/3 its length); (the upper) long relative to the adjacent lemmas; dorsiventral to the rachis; hairless; pointed; awned (the upper caudate-aristate); non-carinate; herbaceous. Lower glume 3 nerved. 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. The proximal incomplete florets male. The proximal lemmas acuminate to shortly awned; awned, or awnless (but then attenuate-mucronate); 5 nerved; herbaceous.
Female-fertile florets 1. Lemmas ovate-lanceolate; papyraceous; smooth to striate; entire; not crested; awnless; hairless; glabrous (shining); non-carinate; with a clear germination flap; 5 nerved. Palea present; relatively long; entire; awnless, without apical setae; textured like the lemma; 2-nerved; 2-keeled. Palea keels wingless. Lodicules present; 2; free; fleshy; glabrous; not or scarcely vascularized. Stamens 3. Anthers not penicillate. Ovary glabrous. Styles basally fused. Stigmas 2; red pigmented.
Fruit, embryo and seedling. Fruit small to medium sized (about 4 mm long); ellipsoid; longitudinally grooved; compressed dorsiventrally (slightly). Hilum long-linear (nearly as long as the grain). Embryo large; not waisted. Endosperm hard.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Mid-intercostal long-cells having markedly sinuous walls. Microhairs present; panicoid-type. Stomata common. Subsidiaries triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs. Costal short-cells conspicuously in long rows. Costal silica bodies ‘panicoid-type’; cross shaped (mostly), or nodular (few); not sharp-pointed.
Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with radiate chlorenchyma; Isachne-type. Leaf blade with distinct, prominent adaxial ribs to ‘nodular’ in section; with the ribs more or less constant in size. Midrib not readily distinguishable; with one bundle only. Bulliforms present in discrete, regular adaxial groups; in simple fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; forming ‘figures’. Sclerenchyma all associated with vascular bundles.
Cytology. 2n = 20.
Taxonomy. Panicoideae; Panicodae; Paniceae.
Distribution, ecology, phytogeography. 1 species; South America. Hydrophytic, or helophytic.
Neotropical. Pampas.
Rusts and smuts. Smuts from Ustilaginaceae. Ustilaginaceae — Sorosporium.
References, etc. Morphological/taxonomic: Parodi 1937. Leaf anatomical: this project.
Illustrations. • 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).
