Solitary herb growing in very dense tussocks from a short, branched rhizome. All leaves basal. Culms 2–6 cm, slender (0.4–0.7 mm thick), smooth. Entire plant glabrous, pale or yellowish green.
Leaves alternate, ensiform (sharply folded along the mid vein, only the lower surface visible), distichous (in two dense, opposite rows), 1–1.5(2) × 0.1–0.2 cm, much shorter than the culms, linear, abruptly narrowing into an acute or acuminate point, with 3–5 veins, densely papillose with papillae as minute teeth in leaf margins, bases and sheaths pale to whitish. Leafy shoots are entirely flat (as pressed).
Inflorescence a single terminal head per culm, 3–7 × 4–6 mm, with 3–8 subsessile flowers. Each flower subtended by a hyaline bract 0.5–0.7 × 0.2–0.4 mm, bract 3-lobed with 2 minute lateral lobes.
Flowers radially symmetric. Perianth of 3 + 3 tepals, 1.8–2.1 × 0.6–0.8 mm, about as long as gynoecium, narrowly spathulate, white with greenish mid part. Stamens 6; filaments 1–1.5 mm, glabrous; anthers kidney-shaped (reniform), pale yellowish green. Gynoecium of 3 carpels with free, beak-like upper parts, each narrowing into a persistent style, with one room.
Capsule 2.0–2.5 × 1.0–1.3 mm, broadly ellipsoid. Seeds numerous, minute.
Sexual reproduction by seeds; very local vegetative reproduction by fragmentation of rhizome. The very small flowers are probably mainly self pollinated. Seed reproduction is probably rare in Svalbard under prevailing climatic conditions. Most stands have been observed with comparatively few flowering culms and with fruit development arrested at the end of season, retaining unopened and immature fruits into the next season. No mature seeds have been found. However, large populations occur in several sites, a proof that seed reproduction must take place now and then.
Seeds have no special adaptation to dispersal but are light enough for some restricted wind dispersal. Culms become stiff and may support some ballistic dispersal, too.
There is nothing similar in the Svalbard flora, viz. the ensiform leaves.
Dense heath or tussock vegetation on fine-grained substrates with circumneutral or basic soil reaction (pH), often within Cassiope or Dryas heaths with dense moss cover, also in shallow mires with, e.g., Carex parallela, Juncus albescens or Saxifraga aizoides, often associated with some seepage.
Thermophilous. In the middle arctic tundra zone and the weakly and clearly continental sections. Tofieldia pusilla is restricted to the fjord districts of Spitsbergen with 14 known localities. With one exception it is present only north of Isfjorden where it is rather rare at Pyramiden, in the Kapp Wijk area and Nathorstdalen (Dickson Land), at Kapp Smith–Kapp Wærn and the inner parts of Dicksonfjorden (James I Land), at Ossian Sarsfjellet and the Blomstrand area in Kongsfjorden (Haakon VII Land), at Bockfjorden (Haakon VII Land), and in Flatøyrdalen and Ringhorndalen on the middle east side of Wijdefjorden (Ny-Friesland). The exception is an old collection from “Groene Haven”, i.e., Grønfjorden, in W Nordenskiöld Land on the south side of Isfjorden. The largest known populations are found in Nathorstdalen with ca. 1000 individuals (Alsos et al. 2011), in the Kapp Wijk–Idodalen area with several hundreds (R. Elven observ. 1990 & 1997), and at Bockfjorden with ca. 100 individuals (Alsos et al. 2011). Its preference for substrates with a basic soil reaction (pH) restricts its distribution to the northern half of Spitsbergen.
The general range is circumpolar in the arctic and boreal zones and with extensions south to mountains in the temperate zones.
The range in Svalbard is interrupted and seems relict, probably from the warmer parts of the Postglacial (the Hypsithermal). Several plants with a similar distribution pattern have a reduced genetic diversity in Svalbard (Alsos et al. 2007). However, in Tofieldia the level of genetic diversity in Svalbard is at about the same level as found elsewhere (Skjetne 2012). This is a species that could react favourably and rapidly on increased temperatures and length of growth season as it seems to be on the brink of efficient seed reproduction with prevailing temperatures.
Alsos, I.G., Elven, R., Brysting, A.K., Birkeland, S. & Skjetne, I. 2011. Økologiske og genetiske undersøkelser av rødlistearter på Svalbard. – Rapport til Svalbards Miljøvernfond. http://www.sysselmannen.no/Svalbard-environmental-protection-fund/Resultater---rapporter/?q=alsos 45 s.
Alsos, I.G. et al. 2007. Frequent long-distance colonization in the changing Arctic. – Science 316: 1606–1609.
Skjetne, I. 2012. Conservation genetics and ecology of four red listed vascular plant species in the high arctic archipelago of Svalbard. – M.Sc. Thesis, Univ. Oslo, Oslo.