The grass genera of the world
Type species: Type: P. curvifolia (Schrad.) Stapf.
Including Achneria Benth., Afrachneria Sprague, Poagrostis Stapf
Habit, vegetative morphology. Perennial (usually), or annual (less commonly); usually caespitose. Culms 10–150 cm high; herbaceous; branched above, or unbranched above. Culm nodes glabrous. Culm internodes hollow. Plants unarmed; with multicellular glands, or without multicellular glands (present in various forms, sometimes sunken, in about half the species). Young shoots intravaginal. The shoots aromatic (or foetid), or not aromatic. Leaves mostly basal (usually), or not basally aggregated; non-auriculate. Leaf blades linear to lanceolate (or filiform, often with multicellular, stalked or saucer-shaped glands); narrow; 0.5–5 mm wide; setaceous, or not setaceous; rolled (usually), or flat; exhibiting multicellular glands abaxially (at the base of macrohairs). The abaxial leaf blade glands intercostal. Leaf blades without cross venation; persistent. Ligule a fringe of hairs. Contra-ligule present (rarely, as a fringe of hairs), or absent.
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets; without hidden cleistogenes.
Inflorescence. Inflorescence few spikeleted, or many spikeleted; paniculate (the branches often with glands); open, or contracted (sometimes spicate); with capillary branchlets, or without capillary branchlets; espatheate; not comprising partial inflorescences and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund; pedicellate.
Female-fertile spikelets. Spikelets 1–19 mm long; compressed laterally; disarticulating above the glumes; disarticulating between the florets; with conventional internode spacings. Rachilla prolonged beyond the uppermost female-fertile floret (as a minute bristle, or with a rudimentary third floret), or terminated by a female-fertile floret; the rachilla extension (when present) with incomplete florets, or naked. Hairy callus present. Callus short; blunt.
Glumes two; more or less equal; about equalling the spikelets to exceeding the spikelets; long relative to the adjacent lemmas (enclosing the spikelet); hairy, or hairless; glabrous; pointed; awnless; carinate; similar (narrow to lanceolate, green or scarious, rarely hyaline, shining, often with glands). Lower glume much exceeding the lowest lemma (usually), or about equalling the lowest lemma; 1 nerved (above the base). Upper glume 1 nerved (above the base). Spikelets occasionally with incomplete florets, or with female-fertile florets only (usually). The incomplete florets when present, distal to the female-fertile florets. The distal incomplete florets merely underdeveloped.
Female-fertile florets 2. Lemmas similar in texture to the glumes (membranous); not becoming indurated; incised (bifid, rarely 3–4-fid); 2 lobed, or 4–5 lobed (rarely); not deeply cleft; awnless, or mucronate, or awned (generally awned from the central sinus, and with a point or straight awn on each lobe). Awns when present, 1 (rarely), or 3 (usually), or 5 (rarely); median, or median and lateral (usually); the median different in form from the laterals (when laterals present); from a sinus; usually geniculate; hairless; much longer than the body of the lemma; entered by several veins (two or three). The lateral awns when present, shorter than the median (straight, inserted in the sinuses and partially fused to the lateral lemma lobes). Lemmas hairy, or hairless; non-carinate (dorsally rounded); without a germination flap; 5–7 nerved; with the nerves non-confluent. Palea present; relatively long; tightly clasped by the lemma; apically notched; awnless, without apical setae; textured like the lemma; not indurated (thinly membranous); 2-nerved (but with the nerves not reaching the apex of the palea); 2-keeled (with the keels very poorly developed). Palea keels wingless; glabrous. Lodicules present; 2; free; fleshy; ciliate, or glabrous. Stamens 3. Anthers not penicillate; without an apically prolonged connective. Ovary apically glabrous. Styles free to their bases. Stigmas 2; white.
Fruit, embryo and seedling. Fruit small; golden-brown; ellipsoid; longitudinally grooved; glabrous; smooth. Hilum short (but linear-oblong). Pericarp free, or fused, or loosely adherent. Embryo large to small (up to a third of the grain length).
Ovule, embryology. Micropyle oblique (P. pungens), or not noticeably oblique (mostly). Outer integument covering no more than the chalazal half of the ovule; more than two cells thick at the micropylar margin, or two cells thick at the micropylar margin. Inner integument discontinuous distally (mostly), or continuous, the micropyle constricted (P. pungens); not thickened around the micropyle (mostly), or thickened around the micropyle (P. pungens). Synergids haustorial (strongly or weakly developed), or not haustorial; without large, globular starch grains (mostly), or exhibiting large, globular starch grains (P. chippendalliae).
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 (but the costals slightly thicker walled). Mid-intercostal long-cells rectangular, or rectangular and fusiform (Poagrostis); having markedly sinuous walls. Microhairs present; elongated; clearly two-celled; panicoid-type. Microhair apical cell wall thinner than that of the basal cell and often collapsed. Microhairs 42–45(–54) microns long, or 54–57 microns long (Poagrostis). Microhair basal cells 24–27 microns long. Microhairs 5.4–11.4 microns wide at the septum. Microhair total length/width at septum 5–10. Microhair apical cells (16.5–)19.5–21(–22.5) microns long, or 28.5–34.5 microns long (Poagrostis). Microhair apical cell/total length ratio 0.39–0.49, or 0.53–0.6 (Poagrostis). Stomata common, or absent or very rare (Poagrostis); 24–39 microns long. Subsidiaries dome-shaped. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells fairly common (Poagrostis), or absent or very rare; when present, in cork/silica-cell pairs (and solitary). Intercostal silica bodies absent. Costal short-cells conspicuously in long rows. Costal silica bodies present in alternate cell files of the costal zones; panicoid-type; mostly dumb-bell shaped, or dumb-bell shaped and nodular; not sharp-pointed.
Transverse section of leaf blade, physiology. Lamina mid-zone in transverse section open.
C3; XyMS+. Mesophyll with non-radiate chlorenchyma; without adaxial palisade. Leaf blade with distinct, prominent adaxial ribs; with the ribs more or less constant in size. Midrib conspicuous, or not readily distinguishable (Poagrostis); with one bundle only. Bulliforms present in discrete, regular adaxial groups; in simple fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; forming figures. Sclerenchyma all associated with vascular bundles. The lamina margins with fibres (few cells), or without fibres.
Cytology. Chromosome base number, x = 7 and 13. 2n = 14, 26, 28, 42, and 52.
Classification. Watson & Dallwitz (1994): Arundinoideae; Danthonieae. Soreng et al. (2015): Danthonioideae; Danthonieae. About 65 species.
Distribution, phytogeography, ecology. Africa, Madagascar.
Commonly adventive. Xerophytic, or mesophytic; species of open habitats; glycophytic.
Economic aspects. Significant weed species: P. thunbergii. Important native pasture species: P. borussica.
References, etc. Leaf anatomical: studied by us - P. airoides (Nees) Stapf, P. pusilla.
Illustrations. • P. malouinensis, as Airopsis steudelii: Kunth (1835). • P. curvifolia, as Pentameris: Kunth (1835). • P. triseta, as Danthonia thunbergii: Kunth (1835). • P. airoides: Gardner, 1952. • P. capillaris, as Achneria: Hook. Ic. Pl. 27 (1901). • General aspect (P. airoides): Gibbs Russell et al., 1990
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’.