The grass genera of the world
Type species: Type: P. pratense L.
Including Achnodon Link, Achnodonton P. Beauv., Chilochloa P. Beauv., Heleochloa P. Beauv., Phalarella Boiss., Plantinia Bub., Stelephuros Adans.
Excluding Maillea, Pseudophleum
Habit, vegetative morphology. Annual, or perennial; rhizomatous, or stoloniferous, or caespitose, or decumbent. Culms 4–150 cm high; herbaceous; sparsely branched above, or unbranched above. The branching simple. Culms tuberous, or not tuberous. Culm nodes glabrous. Culm internodes hollow. Leaves not basally aggregated; non-auriculate. Leaf blades linear; apically cucullate; narrow; 1–10 mm wide; usually flat; not pseudopetiolate; without cross venation; persistent; rolled in bud. Ligule present; an unfringed membrane; truncate, or not truncate; 1.5–6 mm long.
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets; outbreeding and inbreeding.
Inflorescence. Inflorescence paniculate; contracted; capitate, or more or less ovoid, or spicate; espatheate; not comprising partial inflorescences and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund.
Female-fertile spikelets. Spikelets 1.6–5 mm long; strongly compressed laterally; disarticulating above the glumes. Rachilla prolonged beyond the uppermost female-fertile floret, or terminated by a female-fertile floret; the rachilla extension when present, naked. Hairy callus absent. Callus short.
Glumes two; more or less equal; long relative to the adjacent lemmas (exceeding them); pointed; shortly awned; carinate; similar (membranous, the margins overlapping for most of their length). Lower glume 3 nerved. Upper glume 3 nerved. Spikelets with female-fertile florets only; without proximal incomplete florets.
Female-fertile florets 1. Lemmas less firm than the glumes (membranous); not becoming indurated; entire; blunt (truncate or obtuse); awnless; hairy, or hairless (glabrous to densely ciliate); non-carinate; 5–7 nerved. Palea present; relatively long; entire to apically notched; awnless, without apical setae; not indurated; 1-nerved, or 2-nerved; keel-less. Lodicules present; 2; free; membranous; glabrous; toothed; not or scarcely vascularized. Stamens 3. Anthers 0.3–2.3 mm long; not penicillate. Ovary apically glabrous. Styles fused, or free to their bases. Stigmas 2.
Fruit, embryo and seedling. Fruit small. Hilum short. Embryo small; not waisted. Endosperm liquid in the mature fruit; containing compound starch grains. Embryo with an epiblast; without a scutellar tail; with a negligible mesocotyl internode. Embryonic leaf margins meeting.
Seedling with a long mesocotyl; with a loose coleoptile, or with a tight coleoptile. First seedling leaf with a well-developed lamina. The lamina broad, or narrow; erect; 3 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. Mid-intercostal long-cells fusiform; having markedly sinuous walls. Microhairs absent. Stomata common; (36–)42–45 microns long. Subsidiaries parallel-sided. Guard-cells overlapped by the interstomatals. Intercostal short-cells absent or very rare (rare); not paired (usually solitary); not silicified. Crown cells absent (but some reduced prickles approach these). Costal short-cells conspicuously in long rows. Costal silica bodies horizontally-elongated crenate/sinuous, or horizontally-elongated smooth, or rounded; not sharp-pointed.
Transverse section of leaf blade, physiology. 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; with one bundle only. Bulliforms present in discrete, regular adaxial groups; in simple fans. Many of the smallest vascular bundles unaccompanied by sclerenchyma, or all the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; nowhere forming figures. Sclerenchyma all associated with vascular bundles.
Phytochemistry. Tissues of the culm bases with little or no starch. Fructosans predominantly long-chain. Leaves without flavonoid sulphates (2 species).
Cytology. Chromosome base number, x = 7. 2n = 10 (rarely), or 14, or 28, or 42. 2, 4, and 6 ploid. Chromosomes large. Haploid nuclear DNA content 1.6–1.7 pg (2 species). Mean diploid 2c DNA value 3.4 pg (1 species).
Classification. Watson & Dallwitz (1994): Pooideae; Poodae; Aveneae. Soreng et al. (2015): Pooideae; Poodae; Poeae; Poinae. 15 species.
Distribution, phytogeography, ecology. Temperate Eurasia, America.
Commonly adventive. Mostly mesophytic; species of open habitats; mostly glycophytic, or halophytic. Meadows and dry places, P. arenarium in coastal sand.
Economic aspects. Cultivated fodder: P. bertolonii, P. pratense (Timothy). Lawns and/or playing fields: P. bertolonii.
Rusts and smuts. Rusts Puccinia. Taxonomically wide-ranging species: Puccinia graminis, Puccinia coronata, Puccinia striiformis, Puccinia brachypodii, Puccinia poarum, and Uromyces dactylidis. Smuts from Tilletiaceae and from Ustilaginaceae. Tilletiaceae Entyloma, Tilletia, and Urocystis. Ustilaginaceae Ustilago.
References, etc. Leaf anatomical: Metcalfe 1960 and this project.
Illustrations. • P. pratense: Gardner, 1952. • P. phleoides (as P. boehmeri): general aspect, Eng. Bot. (1872). • P. pratense, general aspect: Eng. Bot. (1872). • P. alpinum, general aspect: Eng. Bot. (1872). • P. arenarium, general aspect: Eng. Bot. (1872). • Pollen antigens: Watson and Knox (1976)
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’.