Orthoclada P. Beauv.
Habit, vegetative morphology. Perennial; rhizomatous, or caespitose. The flowering culms leafy. Culms 80–180 cm high; herbaceous; to 0.4 cm in diameter; branched above. Culm nodes glabrous. Culm internodes hollow. Plants unarmed. Leaves not basally aggregated; auriculate; with auricular setae. Leaf blades lanceolate to elliptic; broad; pseudopetiolate; cross veined; rolled in bud; ligule present; an unfringed membrane (minutely ciliolate); truncate; 0.5–1 mm long. Contra-ligule absent.
Reproductive organization. Plants bisexual, with bisexual spikelets; with hermaphrodite florets.
Inflorescence. Inflorescence paniculate, or of spicate main branches (then the primary branches reduced to open racemes); open; with capillary branchlets; espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets solitary; pedicellate.
Female-fertile spikelets. Spikelets 4–12 mm long; compressed laterally; falling with the glumes. Rachilla prolonged beyond the uppermost female-fertile floret (adherent to the lower back of the palea); hairy (minutely); the rachilla extension with incomplete florets. Hairy callus absent.
Glumes two; very unequal (G1 about 2/3 the length of G2); shorter than the adjacent lemmas; free; hairless (sparsely scabrid); pointed; awnless; carinate (somewhat); similar (lanceolate, herbaceous-membranous). Lower glume 3–5 nerved. Upper glume 3–5 nerved. Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets. The distal incomplete florets merely underdeveloped. Spikelets without proximal incomplete florets.
Female-fertile florets 1–5 (decreasing in size acropetally). Lemmas acuminate; similar in texture to the glumes to decidedly firmer than the glumes; not becoming indurated; entire; pointed; awnless; hairless (sparsely scabrid above); slightly carinate; 5–6 nerved. Palea present; relatively long; apically notched (minutely); awnless, without apical setae; textured like the lemma; not indurated; 2-nerved (but folded, bringing the keels together); 2-keeled (the keels joined to the lower part of the internode above). Palea keels minutely winged (above, and the internode above situated in the groove between them). Lodicules present; 2; free; fleshy; glabrous; not toothed; heavily vascularized. Stamens 2 (O. laxa), or 3. Anthers not penicillate; without an apically prolonged connective. Ovary glabrous. Styles free to their bases. Stigmas 2.
Fruit, embryo and seedling. Fruit free from both lemma and palea; small; compressed laterally. Hilum short. Embryo large; with an epiblast; with a scutellar tail; with an elongated mesocotyl internode. Embryonic leaf margins overlapping.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells markedly different in shape costally and intercostally (the costals relatively much longer); of similar wall thickness costally and intercostally (thin walled). Intercostal zones with typical long-cells (though with some rather short). Mid-intercostal long-cells rectangular; having markedly sinuous walls (very deeply so). Microhairs present; panicoid-type; (46.5–)57–60 microns long; 3–3.6 microns wide at the septum. Microhair total length/width at septum 12.9–20. Microhair apical cells (28.5–)34.5–37.5(–39) microns long. Microhair apical cell/total length ratio 0.58–0.66. Stomata common; (30–)36–39 microns long. Subsidiaries triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells absent or very rare. Costal short-cells conspicuously in long rows. Costal silica bodies ‘panicoid-type’; mostly cross shaped, butterfly shaped, and dumb-bell shaped; not sharp-pointed.
Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with adaxial palisade; seemingly without arm cells (but material seen poor); with fusoids (shortish). The fusoids an integral part of the PBS. Leaf blade with the ribs more or less constant in size. Midrib conspicuous; having a conventional arc of bundles (one large bundle, two small laterals); with colourless mesophyll adaxially. Bulliforms present in discrete, regular adaxial groups (these large); in simple fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders absent (adaxial strand-abaxial girder combinations only). Sclerenchyma all associated with vascular bundles.
Cytology. Chromosome base number, x = 12. 2n = 24. 2 ploid.
Taxonomy. Centothecoideae; Centotheceae.
Distribution, ecology, phytogeography. 2 species; 1 in southern Mexico to tropical South America and West Indies; 1 in southeastern tropical Africa. Shade species; glycophytic. In forests.
Paleotropical and Neotropical. African. Sudano-Angolan and West African Rainforest. Caribbean, Amazon, Central Brazilian, and Andean. South Tropical African.
References, etc. Leaf anatomical: this project.
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).