The grass genera of the world
Habit, vegetative morphology. Perennial; rhizomatous. The flowering culms leafy. Culms herbaceous; unbranched above. Culm internodes solid. Rhizomes leptomorph. Plants unarmed. Leaves not basally aggregated. Leaf blades elliptic, or obovate; broad; pseudopetiolate (becoming inverted by twising of the petiole); pinnately veined (the nerves running obliquely from mid-rib to margin); cross veined. Contra-ligule absent.
Reproductive organization. Plants monoecious with all the fertile spikelets unisexual; without hermaphrodite florets. The spikelets of sexually distinct forms on the same plant; female-only and male-only. The male and female-fertile spikelets mixed in the inflorescence. The spikelets overtly heteromorphic (the females larger).
Inflorescence. Inflorescence paniculate ((1-)3–8 noded, fragile); open; non-digitate. Inflorescence axes not ending in spikelets (apically), or with axes ending in spikelets. Inflorescence espatheate (no subtending bracts with the spikelet branchlets); not comprising partial inflorescences and foliar organs. Spikelet-bearing axes disarticulating; falling entire (the primary branches breaking away from the main rachis). Spikelets paired; not secund; sessile and pedicellate, or subsessile and pedicellate (the pistillate pedicels filiform); consistently in long-and-short combinations. The shorter spikelets female-only. The longer spikelets male-only.
Female-sterile spikelets. Male spikelets smaller, laterally compressed, with 2 glumes; stamens 6 per floret. The floret persistent. The male spikelets with glumes; 1 floreted. Male florets 6 staminate.
Female-fertile spikelets. Spikelets not noticeably compressed (terete); falling with the glumes. Rachilla terminated by a female-fertile floret.
Glumes two to several (occasionally 3); more or less equal; shorter than the adjacent lemmas to long relative to the adjacent lemmas; pointed (acute); awnless; similar (membranous, persisitent). Lower glume 5 nerved. Upper glume 7 nerved. Spikelets with female-fertile florets only; without proximal incomplete florets.
Female-fertile florets 1. Lemmas cylindrical, twisted, often with a minute, bent beak, in one species with fused margins; decidedly firmer than the glumes; becoming indurated (rather thin at anthesis, but hardening in fruit); entire; awnless, or mucronate; hairy (with hooked hairs, becoming adhesive in fruit); non-carinate (becoming involute in fruit); having the margins inrolled against the palea; 5–7 nerved. Palea present (very narrow, folded around the long style); relatively long; tightly clasped by the lemma; awnless, without apical setae; not indurated (membranous); 2-nerved; 2-keeled. Lodicules present; 3; free. Stamens 0. Ovary apically glabrous. Styles fused. Stigmas 3.
Fruit, embryo and seedling. Hilum long-linear. Endosperm hard; without lipid; containing compound starch grains. Embryo with an epiblast; with a scutellar tail, or without a scutellar tail. Embryonic leaf margins overlapping.
First seedling leaf with a well-developed lamina.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells markedly different in shape costally and intercostally (the costals very long, narrow, straight-walled, fibre-like with tapered ends). Mid-intercostal long-cells rectangular; having markedly sinuous walls (thin). Microhairs absent. Stomata common (but relatively infrequent, alongside the veins); 24–25.5–27 microns long. Subsidiaries parallel-sided to dome-shaped (high domes to tall parallels). 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; cross shaped to dumb-bell shaped; not sharp-pointed.
Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with arm cells; with fusoids. The fusoids external to the PBS. Leaf blade adaxially flat. Midrib conspicuous; having complex vascularization; with colourless mesophyll adaxially. Bulliforms present in discrete, regular adaxial groups (also in rather irregular groups); in simple fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present (some; others with only strands). Sclerenchyma all associated with vascular bundles.
Culm anatomy. Culm internode bundles scattered.
Special diagnostic feature. Not having female spikelets as in Leptaspis and Scrotochloa (q.v.).
Cytology. Chromosome base number, x = 12. 2n = 24 and 48. 2 and 4 ploid.
Classification. Watson & Dallwitz (1994): Bambusoideae; Oryzodae; Phareae. Soreng et al. (2015): Pharoideae; Phareae. 6 species.
Distribution, phytogeography, ecology. Tropical America, West Indies.
References, etc. Leaf anatomical: Metcalfe 1960; studied by us - P. latifolius L.
Special comments. Fruit data wanting. Illustrations. • P. latifolius: Hitchcock (1936), W.I. Grasses.. • P. latifolius: P. Beauv. (1812). • P. lappulaceus: Nicora & Rúgolo de Agrasar (1987)
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. delta-intkey.com/grass’.