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The grass genera of the world

L. Watson, T.D. Macfarlane, and M.J. Dallwitz

Peyritschia Fourn.

~ Trisetum: e.g., P.koelerioides (Peyr.) Fourn. (= Trisetum altijugum (Fourn.) Scribn.), P. pringlei Scribn. (= Trisetum kochianum I. Hdz. T.). See Hernandez and Koch 1987

Habit, vegetative morphology. Perennial. Culms herbaceous; often decumbent. Culm internodes hollow. Young shoots extravaginal. Leaves non-auriculate. Leaf blades narrow; without cross venation; persistent. Ligule an unfringed membrane; truncate.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets.

Inflorescence. Inflorescence paniculate; open to contracted; espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund; pedicellate.

Female-fertile spikelets. Spikelets compressed laterally; disarticulating above the glumes (?). Rachilla prolonged beyond the uppermost female-fertile floret; hairy to hairless.

Glumes two; more or less equal; about equalling the spikelets; long relative to the adjacent lemmas; pointed; awnless; carinate; similar. Spikelets with female-fertile florets only, or with incomplete florets. The incomplete florets if present, distal to the female-fertile florets.

Female-fertile florets 2. Lemmas similar in texture to the glumes; not becoming indurated; incised; 2 lobed (the lobes rounded or erose); not deeply cleft; mucronate (the awn sometimes rudimentary), or awned. Awns when present, 1; median; dorsal; from near the top, or from well down the back; non-geniculate, or geniculate; much shorter than the body of the lemma to about as long as the body of the lemma; entered by one vein. Palea present; relatively long; tightly clasped by the lemma; with apical setae; 2-nerved; 2-keeled. Lodicules present; 2; free; membranous; toothed. Stamens 2 (Clayton and Renvoize 1986). Styles free to their bases. Stigmas 2.

Fruit, embryo and seedling. Fruit compressed dorsiventrally. Hilum short. Pericarp thin (shining). Embryo small. Endosperm liquid in the mature fruit.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells markedly different in shape costally and intercostally (the costals narrower); differing markedly in wall thickness costally and intercostally (the costals thicker walled). Mid-intercostal long-cells fusiform; having straight or only gently undulating walls. Microhairs absent. Stomata common to absent or very rare. Subsidiaries parallel-sided to dome-shaped. Guard-cells overlapped by the interstomatals. Intercostal short-cells absent or very rare (excluding the bases of prickles). Costal short-cells neither distinctly grouped into long rows nor predominantly paired (solitary, paired and in short rows), or conspicuously in long rows (in places, in P. koelerioides). Costal silica bodies present and well developed; horizontally-elongated crenate/sinuous (crenate); 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 (low, round topped). Midrib not readily distinguishable; with one bundle only. The lamina symmetrical on either side of the midrib. Bulliforms present in discrete, regular adaxial groups (one in each furrow); in simple fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; forming ‘figures’ (all the major bundles with substantial I’s or T’s). Sclerenchyma all associated with vascular bundles.

Special diagnostic feature. Panicle loose, or if dense then interrupted, neither cylindrical nor ovoid: awns usually present, usually twisted, usually distinctly dorsal, conspicuous if inflorescence compact.

Cytology. Chromosome base number, x = 7. 2n = 28. 4 ploid.

Classification. Watson & Dallwitz (1994): Pooideae; Poodae; Aveneae. Soreng et al. (2015): Pooideae; Poodae; Poeae; Aveninae. 5 species (P. conferta, P. deyeuxioides, P. humilis, P. koelerioides, P. pringlei).

Distribution, phytogeography, ecology. Mexico.

Rusts and smuts. Rusts — Puccinia. Taxonomically wide-ranging species: Puccinia poarum.

References, etc. Morphological/taxonomic: Koch 1979. Leaf anatomical: this project.

Illustrations. • P. deyeuxioides, as Avena: Humboldt, Bonplace & Kunth (1825), Nova genera et species plantarum 7


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’.

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