The grass genera of the world
Habit, vegetative morphology. Annual, or perennial. Culms herbaceous. Leaf blades narrow (very); not setaceous (flat or involute); flat, or rolled (involute); without cross venation. Ligule an unfringed membrane.
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets of sexually distinct forms on the same plant; hermaphrodite and male-only, or hermaphrodite and sterile; overtly heteromorphic; in both homogamous and heterogamous combinations (one male or neuter pair, inconspicuous, at the base of the lower raceme).
Inflorescence. Inflorescence of spicate main branches (a single raceme or raceme-pair), or paniculate (then a scanty, spatheate false panicle of racemes); with capillary branchlets (i.e., the articles of racemes and peduncles); spatheate; a complex of partial inflorescences and intervening foliar organs, or not comprising partial inflorescences and foliar organs (when comprising only two racemes). Spikelet-bearing axes racemes (the rachis few to many-jointed); paired (not deflexed, the bases terete, unequal, the upper filiform); with very slender rachides; disarticulating; disarticulating at the joints. Articles linear; not appendaged (by contrast with Hyperthelia); disarticulating obliquely; somewhat hairy (ciliate on both sides). Spikelets paired; sessile and pedicellate; consistently in long-and-short combinations; in pedicellate/sessile combinations. Pedicels of the pedicellate spikelets free of the rachis. The shorter spikelets hermaphrodite (sometimes male or sterile in the lowermost pair). The longer spikelets male-only, or sterile.
Female-sterile spikelets. The pedicelled spikelets about as long as the sessile, narrowly lanceolate, male with two hyaline lemmas or empty. Callus small and oblong or absent. Pedicel ciliate on both sides.
Female-fertile spikelets. Spikelets 4.5–12 mm long; not noticeably compressed to compressed dorsiventrally (subterete); falling with the glumes (falling with adjacent joint and pedicel). Rachilla terminated by a female-fertile floret. Hairy callus present (long, pointed, curved or oblique). Callus long; pointed.
Glumes two; more or less equal; long relative to the adjacent lemmas; hairless (glabrous, or the margins ciliate); (the upper) awned (or at least aristulate); carinate (G2), or non-carinate (G1); very dissimilar (the lower with a dorsal median groove and narrow involute margins, sub-keeled upwards and sometimes winged, bidentate and bimucronate, the upper cymbiform, awned or aristulate). Lower glume two-keeled (with a dorsal median groove); sulcate on the back (without a conspicuous herbaceous tip, by contrast with Hyperthelia); not pitted; relatively smooth. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. Spikelets with proximal incomplete florets. The proximal incomplete florets 1; sterile. The proximal lemmas awnless (narrow-lanceolate); similar in texture to the female-fertile lemmas (hyaline); not becoming indurated.
Female-fertile florets 1. Lemmas stipitate below; less firm than the glumes (hyaline); not becoming indurated; incised; 2 lobed (bidentate); awned. Awns 1; median; from a sinus; geniculate; hairy; much longer than the body of the lemma. Lemmas non-carinate; without a germination flap; 1 nerved. Palea present, or absent; when present, very reduced. Lodicules present; 2; free; glabrous. Stamens 3 (the anthers rather long). Ovary apically glabrous. Stigmas 2.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous (the intercostal zones very narrow). Papillae present; intercostal (on each interstomatal cell). Intercostal papillae over-arching the stomata (slightly, in places), or not over-arching the stomata (for the most part); consisting of one oblique swelling per cell, or consisting of one symmetrical projection per cell. Long-cells of similar wall thickness costally and intercostally (thin walled). Mid-intercostal long-cells rectangular; having markedly sinuous walls and having straight or only gently undulating walls (the sinuosity very fine). Microhairs present; elongated; clearly two-celled; panicoid-type. Stomata common. Subsidiaries non-papillate; dome-shaped. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs; silicified. Intercostal silica bodies cross-shaped (and short dumb-bell shaped). No macrohairs or prickles seen. Costal short-cells conspicuously in long rows. Costal silica bodies present and well developed; panicoid-type; dumb-bell shaped (mostly), or nodular (a few).
Transverse section of leaf blade, physiology. Leaf blades largely consisting of midrib, or laminar.
C4. The anatomical organization conventional. XyMS. PCR sheath outlines uneven. Mesophyll traversed by columns of colourless mesophyll cells (in places). Midrib conspicuous; having a conventional arc of bundles (an abaxial arc, with a median primary and small bundles on either side, or three primaries with small bundles between them); with colourless mesophyll adaxially. The lamina symmetrical on either side of the midrib. Bulliforms present in discrete, regular adaxial groups; associated with colourless mesophyll cells to form deeply-penetrating fans; associating with colourless mesophyll cells to form arches over small vascular bundles. Many of the smallest vascular bundles unaccompanied by sclerenchyma (though many of the tiniest have minute abaxial sclerenchyma groups). Combined sclerenchyma girders present (with the primaries). Sclerenchyma all associated with vascular bundles.
Classification. Watson & Dallwitz (1994): Panicoideae; Andropogonodae; Andropogoneae; Andropogoninae. Soreng et al. (2015): Panicoideae; Andropogonodae; Andropogoneae. 5 species.
Distribution, phytogeography, ecology. Tropical Africa and Thailand.
Species of open habitats. Savanna grassland, pools on rock outcrops.
References, etc. Morphological/taxonomic: Clayton 1966. Leaf anatomical: studied by us - P. annua (Hack.) W.D. Clayton.
Special comments. Fruit data wanting. Illustrations. • P. annua: Rose Innes, Ghana Grasses (1977)
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’.