Solitary graminoid herb with all branching inside leaf sheaths (intravaginal). Flowering shoots ascending or erect. Culms 5–12 cm, smooth. Base of aerial shoots without prophylls or sheaths of withered leaves.

Leaves 3–10 cm long, 1–1.5(3) mm broad, tapering towards apex, keeled, flat, scabrous in margin and sometimes on lower surface veins in the apical part, green. Culm leaves 2–3, similar to basal leaves. Ligula 0.5–3 mm, obtuse to truncate.

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 an open, pyramidal panicle with branches to three sides (to four sides in all other Svalbard species of Poa), 1.5–4 cm long, branches spreading, occupying 1/3–1/4 of culm length. Panicle with 5–7 nodes, with ca. 2 branches at each of the lower nodes, smooth. Branches 1–2 cm long, the lower ones with 3–4 spikelets along much of their length. Spikelets 3.5–4.5 × 0.8–1.3 mm, with 3(4) flowers, the uppermost flower(s) often non-functional. Bracts (glumes and lemmas) with keels. Glumes lanceolate, acute, smooth, green or reddish with white hyaline margin, distinctly unequal; lower glume 1.8–2.2 mm with 1 vein; upper glume 2.3–2.7 mm, ca. 1/2 as long as spikelet or more, with 3 veins. Lemmas 2.8–3.5 mm, lanceolate, acute, with 5 more or less distinct veins with curly (crisped) hairs at base of veins, smooth, green or tinged reddish–purplish with white hyaline margin. No callus hairs at base of lemmas. Paleas shorter than lemmas, with softly pubescent keels. Anthers 0.6–1.0 mm, well developed.

Fruit an achene (with one seed).

Sexual reproduction by seeds; no vegetative reproduction. Wind pollinated (and probably also self pollinated). Seed development and reproduction not observed in Svalbard (but may have been overlooked).

Fruits (inside florets) seem to be very easily dispersed with animals and people (feet and footwear).

Non-flowering plants of the mainly annual Poa annua may be nearly impossible to keep apart from seedlings of perennial species; however, such seedlings are not common. Otherwise, the annual or biennial life span, the panicle with branches to three sides only, the distinctly unequal glumes, and the short anthers (up to 1 mm) distinguish Poa annua from all other species of Poa one may expect to find in Svalbard. All the other species of Poa in Svalbard are perennial and have withered leaves and intra- or extravaginal branches.

On disturbed ground within settlements.

Mainly introduced. Recorded from three sites on Spitsbergen: Sigridholmen 1958, one of the Lovén Islands in Kongsfjorden (Haakon VII Land), Barentsburg 1988, 1993, 2008, and Hotellneset 2013 near Longyearbyen (both Nordenskiöld Land). In Barentsburg it may have a permanent population. It may have been overlooked in other settlements. The record from Sigridholmen is enigmatic as there is no obvious connection to the nearby settlement of Ny-Ålesund. The barnacle geese arriving to nest on the Lovén Islands have all rested and changed feathers in springtime on the Helgeland islands in N Norway, a region where P. annua is common, also in the geese pastures on uninhabited skerries and islands. Bird dispersal is a distinct possibility, and if so, the occurrence on Sigridholmen is to be defined as native, albeit probably ephemeral.

This species is hardy, reproducing up to the middle alpine belt in Scandinavia at 1300 m a.s.l. or more, and should be able to reproduce in Svalbard. It is one of the most widespread of all ruderal plants in the world, also into the colder zones as the subantarctic islands and the Antarctic Peninsula (Chown et al. 2012).

The rarity of records of this species in Svalbard, especially in the older material where some investigators thoroughly studied the settlements and their garbage heaps (e.g., O.A. Høeg and J. Lid in 1928, E. Hadač in 1939) is astounding. The species is hardy enough to reproduce in the middle arctic tundra zone where nearly all Svalbard settlements are located. The only explanation we can think of is that it reacts on the light, i.e., is delayed in its development by the extreme long-day light lasting from snow melt until late August. However, it is a common ruderal in northernmost Norway where 24 hour days last from May to July. Also, it is introduced and with stable populations in Iceland, E and W Greenland, the Polar Urals, the Kanin–Pechora region and in W Alaska (Elven et al. 2011), thus other factors than light might be more important. It may have been overlooked in young development stages.

Chown, S.L., Huiskes, A.H.L., Gremmen, N.J.M., Lee, J.E., Terauds, A., Crosbie, K., Frenot, Y., Hughes, K.A., Imura, S., Kiefer, K., Lebouvier, M., Raymond, B., Tsujimoto, M., Ware, C., Van de Vijver, B. & Bergstrom, D.M. 2012. Continent-wide risk assessment for the establishment of nonindigenous species in Antarctica. – Proceedings of the National Academy of Sciences 109: 4938–4943. Doi 10.1073/pnas.1119787109.

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

Hadač, E. 1941. The introduced flora of Spitsbergen. – Det Kongelige Departementet for Handel, Sjøfart, Industri, Håndverk og Fiskeri. 49 pp.

Høeg, O.A. & Lid, J. 1929. Adventive plants in Spitsbergen. – Kongelige Norske Videnskabers Selskabs Forhandlinger I(59): 176-178.