Solitary graminoid herb growing in dense or loose tussocks with all branching inside leaf sheaths (intravaginal, no runners or stolons). Culms 7–25(35) cm, erect, pubescent with retrorse hairs. Base of culms surrounded by a loose sheath of withered leaves.

Leaves pilose on sheaths (with retrorse hairs) and blades, flat, with veins slightly raised on the upper surface, gradually tapering towards apex. Basal leaves 5–12 cm long, shorter than culms, 1.5–2.5 mm broad. Culm leaves ca. 2, similar to basal leaves, with slightly inflated sheaths, flag leaf blade 1–4 cm long, attached around the middle of the culm. Ligula 0.5–2 mm, truncate or rounded, often fringed (erose).

The units of the inflorescence of Poaceae are the spikelets, nearly always numerous in a panicle or spike-like inflorescence. Spikelets are composed of 2 glumes (bracts for the spikelet) and one or more flowers (the term used below) or rather floral units often named ‘florets’ because we do not know what is the exact flower. A flower or floret is composed of a lemma with 1 mid vein (probably the floral bract), a palea with 2 mid veins (either 2 fused bracteoles or perhaps 2 fused perianth leaves), 3 small organs called ‘lodiculae’ and essential in the opening of the flower at anthesis (possibly transformed perianth leaves or transformed stamens), 3 stamens (mostly), and a gynoecium of 2 fused carpels with 2 feathery stigmas and one seed.

Inflorescence a dense, ovoid or cylindrical panicle sometimes interrupted at base, 2–4(5) × 0.8–1.5 cm, occupying 1/4–1/8 of culm length, variegated in dark violet and dark golden yellow. Panicle with numerous nodes with 4–8 branches at each of the lower nodes. Branches ascending, 8–2 mm, pubescent like the mid axis of the panicle but with shorter hairs, each branch with 5–10 spikelets along its entire length. Spikelets 4–6 × 1.5–2 mm (awns excluded), subsessile, with 2(3) flowers. Bracts (glumes and lemmas) with keels. Glumes oblong or lanceolate, acute, 1-veined, scarious on the keel, otherwise smooth and glabrous, without awn, mid section green or purple–violet, otherwise purple–violet except for a broad, bronze yellow hyaline margin; lower glume 2.5–4 mm, upper glume 3–5 mm, 3/4–4/5 as long as spikelet. Lemmas 3–5 mm, lanceolate, acute or acuminate with a bifid apex, 1-veined, scarious on keel, otherwise smooth and glabrous, with coloration like the glumes, with a (3)4–6 mm long, geniculate, barbed awn arising from the keel in its upper part (1/2–2/3 of lemma). Paleas about as long as lemmas, hyaline, with 2 veins extending into bristle-like tips. Anthers 0.8–1.3 mm, well developed.

Fruit an achene (with one seed).

Sexual reproduction by seeds; no vegetative reproduction. Wind pollination. Seed production abundant. Seeds germinate to 32 % in an experiment (Alsos et al. 2013). Panicles of previous years are often retained on plants but emptied of flowers which are the diaspore units.

Flowers with fruits have the long, barbed awn that may facilitate dispersal by wind and animals.

Only two Svalbard plants may remotely resemble this species: Alopecurus ovatus and Festuca baffinensis. Alopecurus ovatus has a dense (congested), spike-like panicle but this panicle is covered by silky hairs, whereas the panicle of Trisetum spicatum is glabrous. Alopecurus ovatus also has glabrous culms and leaves whereas Trisetum spicatum has hairy ones. Festuca baffinensis shares the hairy culms with Trisetum spicatum but has much smaller panicles, straight awns that are an extension of the mid vein in the lemma (and not geniculate awns arising from the back of the lemma), and more numerous flowers in the spikelet.

Trisetum spicatum is a species of rather trivial sites ecologically: short or tall grown meadows, snowbeds, and moderately dry disturbed ground. It avoids wet and permanently moist sites but tolerates some water during snow melt. It seems to prefer substrates with a circumneutral or acidic soil reaction (pH) and is fairly rare in areas with exclusively calcareous bedrock.

Trisetum spicatum is probably present in all zones and sections in Svalbard but is not very common. It is absent from Bjørnøya and its main range is on Spitsbergen, only with one recorded site on Edgeøya and one at Lady Franklinfjorden on Nordaustlandet. On Spitsbergen, it is frequent north of Van Keulenfjorden, rare farther south.

The total range of this species is extremely wide, including the entire Arctic, all major temperate mountain ranges, and extending to the Tropics in, e.g., New Guinea and to the southern hemisphere in South America and Australia.

Trisetum spicatum s. lat. is either a very complicated species or an intricate species complex, as could be expected from its very wide range. The designated lectotype is from Switzerland, connecting the name T. spicatum (s. str.) to the European mountain type. This complex is discussed at length by Elven et al. (2011) with numerous references. Two ploidy levels are found: tetraploid 2n = 28 in T. spicatum s. str. and hexaploid 2n = 42 in what Elven et al. (2011) consider as T. molle (Michx.) Kunth (or T. triflorum (Bigelow) Á.Löve & D.Löve). The hexaploids are not known from mainland Europe or Svalbard but contribute significantly to the variation in Iceland, Greenland, North America and N Asia. Some authors recognize several races or species (e.g., Hultén 1954; Jonsell et al. 1975; Soreng et al. 2003; Finot et al. 2004), others only one polymorphic species (e.g., Randall & Hilu 1986; Rumely 2007). No modern, combined morphological and molecular study has been undertaken, as far as we know, and the most extensive morphological study to date, by Randall & Hilu (1986), is based on an extensive morphometry where possibly significant characters may have been swamped by many plastic ones.

The Svalbard plants differ from the European mainland plants in broader and often shorter panicles. This variation has been recognized from NE Asia as T. spicatum ssp. wrangelense V.V.Petrovsky (Petrovsky & Zhukova 1978; diagnosis: "panicle shorter and denser and pubescence longer" [translated here]). We consider the variation not enough to recognize races and regard the Svalbard plants as T. spicatum s. str.

Alsos, I.G., Müller, E. & Eidesen, P.B. 2013. Germinating seeds or bulbils in 87 of 113 tested Arctic species indicate potential for ex situ seed bank storage. – Polar Biology 36: 819–830. Doi 10.1007/s00300-013-1307-7.

Elven, R., Murray, D.F., Razzhivin, V. & Yurtsev, B.A. (eds.) 2011. Annotated Checklist of the Panarctic Flora (PAF) Vascular plants. http://panarcticflora.org/

Finot, V.L., Peterson, P.M., Soreng, R.J. & Zuloaga, F.O. 2004. A revision of Trisetum, Peyritschia, and Sphenopolis (Poaceae: Poöideae: Aveninae) in Mexico and Central America. – Annals of the Missouri Botanical Garden 91: 1–30.

Hultén, E. 1959. The Trisetum spicatum complex. – Svensk Botanisk Tidskrift 53: 203–228.

Jonsell, B., Pálsson, J. & Portén, E.-K. 1975. Variation and affinities of Trisetum spicatum (L.) Richt. s. lat. (Gramineae) in Iceland. – Svensk Botanisk Tidskrift 69: 113–142.

Petrovsky, V.V. & Zhukova, P.G. 1978. Tsitotaksonomicheskii obzov odnodolnikh rastenii ostrava Vrangelya. – Botanicheskii Zhurnal 63: 1258–1273.

Randall, J.L. & Hilu, K.W. 1986. Biosystematic studies of North American Trisetum spicatum (Poaceae). – Systematic Botany 11: 567–578.

Rumely, J.H. 2007. Trisetum Pers. – In: Flora of North America Editorial Committee (eds.), Flora of North America north of Mexico. 24. Magnoliophyta: Commelinidae (in part): Poaceae, part 1: 744–753.

Soreng, R.J., Peterson, P.M., Davidse, G., Judziewicz, E.J., Zuloaga, F.O., Filgueiras, T.S. & Morrone, O. 2003. Catalogue of New World grasses (Poaceae): IV. Subfamily Pooideae. – Contributions from the U.S. National Herbarium 48. 730 pp.