The grass genera of the world
Habit, vegetative morphology. Annual (rarely), or perennial; caespitose. Culms 50–100 cm high; branched above, or unbranched above. Culm nodes exposed; glabrous. Culm leaves present. Young shoots intravaginal. Leaves not basally aggregated. Leaf blades linear; narrow; 2–5 mm wide; flat; without cross venation; persistent. Ligule an unfringed membrane; truncate; about 0.5 mm long. Contra-ligule absent.
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. The male and female-fertile spikelets mixed in the inflorescence. The spikelets overtly heteromorphic; all in heterogamous combinations. Plants seemingly inbreeding (the stamens enclosed within the spikelets, and the racemes enclosed in the spatheoles); seemingly exposed-cleistogamous.
Inflorescence. Inflorescence paniculate; open; with capillary branchlets; spatheate (and spatheolate); a complex of partial inflorescences and intervening foliar organs. Spikelet-bearing axes very much reduced (consisting of a single triplet of which the pedicellate members may be much reduced or rarely missing (or concealed among the callus hairs?), or the triplet preceded by a heterogamous pair); the spikelet-bearing axes with only one spikelet-bearing article, or with 23 spikelet-bearing articles (one or two articles); solitary; disarticulating; disarticulating at the joints (or at the single articulation). Articles linear; without a basal callus-knob; not appendaged; disarticulating obliquely; densely long-hairy to somewhat hairy. Spikelets paired and in triplets, or in triplets (i.e. seemingly always with a more or less readily recognizable terminal triplet); not secund; 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. The longer spikelets male-only, or sterile (with hairy pedicels).
Female-sterile spikelets. The male/sterile spikelets linear-lanceolate, awnless, glabrous, disarticulating transversely. Rachilla of male spikelets terminated by a male floret. The male spikelets with glumes; with proximal incomplete florets. The lemmas awnless. Male florets 1; 3 staminate.
Female-fertile spikelets. Spikelets 4.5–7.5 mm long; compressed dorsiventrally; falling with the glumes. Rachilla terminated by a female-fertile floret. Hairy callus present. Callus fairly long; pointed.
Glumes two; more or less equal; exceeding the spikelets; long relative to the adjacent lemmas (exceeding them); hairy (towards the apex), or hairless; glabrous; without conspicuous tufts or rows of hairs; awned to awnless (the lower muticous or bisubulate, the upper apiculate to long-awned); very dissimilar (both hardened and shiny, the lower rather flat-backed, truncate to bidentate or bisubulate, the upper more or less carinate by accommodation of the pedicels, truncate to emarginate and apiculate to long-awned). Lower glume convex on the back to flattened on the back; with a conspicuous pit (at the base, at least in P. afzeliana and P hamata); relatively smooth; 4–7 nerved (sometimes conspicuously lacking the median). Upper glume 3 nerved. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. Spikelets with proximal incomplete florets. The proximal incomplete florets 1; epaleate; sterile. The proximal lemmas awnless; 0 nerved, or 2 nerved (palea-like); decidedly exceeding the female-fertile lemmas; similar in texture to the female-fertile lemmas (hyaline); not becoming indurated.
Female-fertile florets 1. Lemmas less firm than the glumes (stipitate-winged below, the wings and lobes hyaline); not becoming indurated; incised; 2 lobed; deeply cleft; awned. Awns 1; median; from a sinus; geniculate; much longer than the body of the lemma (12–35 mm long); entered by one vein. Awn bases twisted; not flattened. Lemmas hairless; non-carinate; without a germination flap; 1 nerved. Palea absent. Lodicules present; 2; free; fleshy; ciliate. Stamens 3 (short, included). Anthers about 2.5 mm long; not penicillate; without an apically prolonged connective. Ovary apically glabrous. Styles basally fused; joined below. Stigmas 2.
Fruit, embryo and seedling. Fruit ellipsoid; glabrous. Hilum short. Embryo large.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present; costal and intercostal (P. hamata), or intercostal (P. afzeliana, confined to the interstomatals). Intercostal papillae over-arching the stomata, or not over-arching the stomata; consisting of one oblique swelling per cell to consisting of one symmetrical projection per cell, or consisting of one symmetrical projection per cell (very large, fairly thick walled). Long-cells of similar wall thickness costally and intercostally (fairly thin walled). Intercostal zones exhibiting many atypical long-cells. Mid-intercostal long-cells rectangular to fusiform (or variously irregular); having straight or only gently undulating walls. Microhairs present; elongated; clearly two-celled; panicoid-type; 30–51 microns long; 4–8.4 microns wide at the septum. Microhair total length/width at septum 3.6–8.5. Microhair apical cells 12–22.5 microns long. Microhair apical cell/total length ratio 0.3–0.6. Stomata common; 22–27 microns long. Subsidiaries non-papillate; triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells seemingly absent or very rare (but numerous short long-cells present). Costal short-cells conspicuously in long rows. Costal silica bodies present and well developed; panicoid-type; dumb-bell shaped; not sharp-pointed.
Transverse section of leaf blade, physiology. C4; XyMS. PCR sheath outlines uneven. PCR sheath extensions absent. Leaf blade adaxially flat. Midrib conspicuous; having a conventional arc of bundles (a large median, and 2–3 smaller bundles on either side); with colourless mesophyll adaxially. The lamina symmetrical on either side of the midrib. Bulliforms present in discrete, regular adaxial groups (in places, most obviously in P. afzeliana), or not present in discrete, regular adaxial groups (the epidermis mostly more or less bulliform except over the larger bundles, and the groups irregular in form); in simple fans (in places, especially in P. afzeliana), or associated with colourless mesophyll cells to form deeply-penetrating fans (especially in P. afzeliana); associating with colourless mesophyll cells to form arches over small vascular bundles (often with single colourless cells adjoining the bulliform epidermis on either side of a small bundle). Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders present (with the primaries only); forming figures (the primaries, in P. hamata), or nowhere forming figures. Sclerenchyma all associated with vascular bundles.
Classification. Watson & Dallwitz (1994): Panicoideae; Andropogonodae; Andropogoneae; Andropogoninae. Soreng et al. (2015): cf. Panicoideae (as a synonym); Andropogonodae; Andropogoneae; Anthistiriinae. 4 species.
Distribution, phytogeography, ecology. Tropical West Africa.
Mesophytic; species of open habitats; glycophytic.
References, etc. Leaf anatomical: this project.
Illustrations. • P. afzeliana (as P. arrecta): Jacques-Félix, 1962
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: 13th November 2017. delta-intkey.com/grass’.