Trisetum Pers.
Type species: T. pratense Pers. nom. illeg.
Perennials, tufted or rhizomatous; branching extravaginal or rarely intravaginal. Ligule membranous, truncate or rounded, often ciliolate. Leaf-blades linear, narrow, flat or involute. Inflorescence a contracted to lax panicle. Spikelets 2-several-flowered, laterally compressed; disarticulation above glumes and between lemmas; rachilla usually hairy, prolonged. Glumes unequal to subequal, < to ≈ spikelets, keeled, not awned; lower 1-3-nerved, upper 3-5-nerved. Lemma membranous to thinly coriaceous, 3-7-nerved, keeled, bidentate or bicuspid, dorsally awned from upper ½; awn reflexed, or geniculate (not N.Z. spp.). Palea gaping, silvery, thinner than lemma, 2-keeled. Callus short, hairy. Flowers ⚥, chasmogamous or cleistogamous. Lodicules 2, membranous, glabrous or ciliate. Stamens 3. Ovary glabrous; styles free. Caryopsis slightly compressed laterally; embryo small; hilum short; endosperm liquid. Fig. 10.
Key
c. 85 spp., of temperate regions throughout the world. Meadows, mountain slopes, upland grasslands, weedy places. Endemic spp. 7, indigenous spp. 2.
N.Z. spp. of Trisetum were revised by Edgar, E. N.Z. J. Bot. 36: 539-564 (1998), incorporating the intensive field observations of A. P. Druce. Most species are variable, especially in form of leaf-blade and in culm vesture. In general Trisetum is found in N.Z. on rocky sites: on limestone or marble cliffs, or on bluffs; in alpine herbfield, fellfield or scree; and on ultramafic sites. Three species, T. lasiorhachis, T. lepidum and T. youngii occur in scrub, open forest or tussock grassland.
All species are very variable. Features normally characteristic of a species are not invariably present and it was not feasible to include every variant in the key.