The grass genera of the world
Type species: Type: P. geminatum (Forssk.) Stapf.
Habit, vegetative morphology. Annual, or perennial (often aquatic); rhizomatous, or caespitose to decumbent. Culms herbaceous; sparsely to asmply branched above, or unbranched above. The branching simple. Culm nodes glabrous. Culm leaf sheaths keeled, or compressed. Culm internodes hollow. Young shoots extravaginal (usually?), or intravaginal. Leaves not basally aggregated; non-auriculate. Leaf blades broad, or narrow; flat, or rolled; not pseudopetiolate; parallel veined; without cross venation; persistent; once-folded in bud. Ligule present; a fringed membrane (very narrow), or a fringe of hairs.
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets.
Inflorescence. Inflorescence of spicate main branches to a false spike, with spikelets on contracted axes (the primary branches arranged distichously on the rachis or borne on one side, generally appressed to the rachis, and sometimes greatly reduced). Primary inflorescence branches borne biseriately on one side of the main axis to borne distichously, or inserted all around the main axis (rarely). Inflorescence axes not ending in spikelets (each terminating in a conspicuous or more or less inconspicuous bristle). Inflorescence espatheate; not comprising partial inflorescences and foliar organs. Spikelet-bearing axes racemes, or very much reduced; persistent. Spikelets unaccompanied by bractiform involucres, not associated with setiform vestigial branches (this being the oft quoted distiction from Setaria: however, the terminal spikelet of each branch is associated with the branch-tip bristle, and since the branches may be reduced to single spikelets, the separation is scarcely adequate); solitary, or paired; secund (the inflorescence branches dorsiventral); (when the racemes not greatly reduced) biseriate. Pedicel apices discoid.
Female-fertile spikelets. Spikelets elliptic, or lanceolate, or ovate; abaxial; compressed laterally, or not noticeably compressed, or compressed dorsiventrally; planoconvex; 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 upper) shorter than the adjacent lemmas, or long relative to the adjacent lemmas; dorsiventral to the rachis; awnless; non-carinate. Lower glume 1–5 nerved. Upper glume 5–11 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, or epaleate. Palea of the proximal incomplete florets when present, fully developed to reduced. The proximal incomplete florets male, or sterile. The proximal lemmas resembling the upper glume; awnless; more or less equalling the female-fertile lemmas; less firm than the female-fertile lemmas; not becoming indurated (membranous).
Female-fertile florets 1. Lemmas decidedly firmer than the glumes; rugose; becoming indurated (crustaceous); yellow in fruit, or brown in fruit; entire; pointed; awnless (often apiculate); hairless; non-carinate; having the margins inrolled against the palea; with a clear germination flap; 5 nerved. Palea present; relatively long; entire; awnless, without apical setae; firm, like the lemma; 2-nerved. Lodicules present; 2; free; fleshy; glabrous. Stamens 3. Anthers not penicillate. Ovary apically glabrous. Styles fused, or free to their bases. Stigmas 2.
Fruit, embryo and seedling. Fruit small; ellipsoid to subglobose; compressed dorsiventrally. Hilum short. Embryo large. Endosperm containing only simple starch grains. Embryo without an epiblast; with a scutellar tail; with an elongated mesocotyl internode. Embryonic leaf margins overlapping.
First seedling leaf with a well-developed lamina. The lamina broad; curved; 13–20 veined.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells similar in shape costally and intercostally; of similar wall thickness costally and intercostally (fairly thin walled). Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; panicoid-type; (40.5–)42–72(–81) microns long; (5.4–)5.7–7.5 microns wide at the septum. Microhair total length/width at septum 7.1–12.3. Microhair apical cells (21–)22.5–42(–51) microns long. Microhair apical cell/total length ratio 0.47–0.63. Stomata common; (24–)25.5–30 microns long. Subsidiaries low dome-shaped (sometimes, a few), or triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common, or absent or very rare; in cork/silica-cell pairs (usually), or not paired (a few solitaries); silicified (when paired). Intercostal silica bodies cross-shaped, or crescentic. Costal short-cells conspicuously in long rows. Costal silica bodies panicoid-type; cross shaped, or butterfly shaped, or dumb-bell shaped; not sharp-pointed.
Transverse section of leaf blade, physiology. C4; XyMS. PCR sheath outlines uneven. PCR sheath extensions absent. PCR cell chloroplasts with reduced grana; centrifugal/peripheral. Mesophyll with radiate chlorenchyma. Leaf blade with distinct, prominent adaxial ribs, or nodular in section. Midrib conspicuous, or not readily distinguishable (rarely); with one bundle only to having a conventional arc of bundles (a small bundle under each midrib hinge). Bulliforms present in discrete, regular adaxial groups; in simple fans. Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders present, or absent; nowhere forming figures. Sclerenchyma all associated with vascular bundles.
Culm anatomy. Culm internode bundles in one or two rings.
Phytochemistry. Leaves without flavonoid sulphates (1 species).
Special diagnostic feature. The lower lemma unlike that of Ophiochloa (i.e., without a central hyaline portion bordered by well developed, conspicously ciliate and terminally setose nerves, and without a pair of hygroscopically active setae at the apex). Spikelets awnless, the female-fertile lemmas pointed or apiculate but not mucronate.
Cytology. Chromosome base number, x = 9. 2n = 18, 36, and 54. 2, 4, and 6 ploid.
Classification. Watson & Dallwitz (1994): Panicoideae; Panicodae; Paniceae. Soreng et al. (2015): Panicoideae; Panicodae; Paniceae; Cenchrinae. About 27 species.
Distribution, phytogeography, ecology. In warm regions.
Hydrophytic to mesophytic; shade species and species of open habitats; glycophytic. Swamps, forests, dry slopes.
Economic aspects. Significant weed species: P. flavidum, P. geminatum, P. punctatum. Important native pasture species: P. desertorum, P. geminatum, P. punctatum.
Rusts and smuts. Rusts Puccinia. Taxonomically wide-ranging species: Uromyces setariae-italicae. Smuts from Ustilaginaceae. Ustilaginaceae Sorosporium and Ustilago.
References, etc. Morphological/taxonomic: Webster (1987) and Veldkamp (1994) discuss the problem of generic delimitation, with the latter reducing the Malesian species to Setaria. Leaf anatomical: Metcalfe 1960 and this project.
Special comments. Somewhat marginally separable from Setaria: even the difference in arrangement of primary inflorescence branches seems to be not quite absolute. Illustrations. • P. basicladum: Gardner, 1952. • Inflorescence and spikelet (P. rarum): E. Hickman. • General aspect (P. obtusifolium): Gibbs Russell et al., 1990. • Part of inflorescence, in close-up
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’.