Very small annual herb with a very slender root. Stems 0.5–3.0 cm, erect, simple (in Svalbard), dark purplish, with curved and retrorse, short, white hairs 0.1–0.2 mm. The two lowermost leaves small and undivided cotyledons retained for some time, the next pair ordinary and usually functioning as bracts for the lowermost flowers (in Svalbard). Lowermost internode (above the cotyledons) ca. 5 mm, next internodes ca. 3 mm.

Leaves subopposite (in pairs but at slightly different levels), 5.5–6.5 × 3.2–3.7 mm, with very short petioles or just narrowed at base, ovate to obovate, deeply crenate or incised dentate with 2(3) lobes or teeth per side, lobes or teeth obtuse in lower parts of plant, subacute or acute in upper parts (inflorescence). Mid vein distinct, lateral veins indistinct. Both surfaces usually purple (especially the lower surface) with scattered white hairs, on the uppermost bracts also with a few, very short, stipitate glands (difference from most mainland plants of the species).

Inflorescence a spike-like raceme with ca. 10 subsessile flowers subtended by bracts largely similar to stem leaves. In Svalbard most leaves of a plant function as bracts.

Flowers monosymmetric. Calyx 4–5 × 2–2.5 mm, fused for 2/3 of its length or more, narrowly campanulate with 5 distinct, green or purplish veins and stiff, very short upwards-pointing hairs on the veins, between veins pale green or nearly white but often with dark blotches (a feature typical of this species but much more pronounced in mainland plants than in Svalbard ones), with 5 calyx teeth free for ca. 1.5 mm, narrowly triangular. Corolla ca. 3.5–4.5 mm with a tubular fused part, limb two-lipped with a three-lobed lower lip and a galeate upper lip of two petals, hairy at top of the galea, pale lilac with darker stripes. Stamens 4. Gynoecium of 2 fused carpels with one style. Stigmas and stamens not protruding from the corolla tube.

Fruit a one-roomed elliptic capsule, 3.8–4.2 × 2.5–2.7, with ca. 5 seeds per capsule. Apex emarginate and with cilia along the margin. Seeds ca. 1 × 0.5 mm, oblong, with a pattern of longitudinal strong white stripes and transversal much weaker white stripes.

Sexual reproduction by seeds; no vegetative reproduction. The flowers are adapted to pollination by small bees, wasps and flies but are so small that we would assume self pollination to prevail. However, in two of its three known sites, the abundance of individuals growing close together, nearly forming a carpet of lilac flowers, may easily attract insects. Therefore, we cannot exclude efficient insect pollination. Mature seeds are observed in all three known sites and in nearly all herbarium collections. Annual seed recruitment is essential for this species as no seed bank has been proved. Seeds collected did not germinate in an experiment (Alsos et al. 2013); however, this may not be significant as germination may depend on stratification conditions (Liebst & Schneller 2008) and as the plant is a semiparasite that may depend on some extrusion from the root of host plants. The hosts are numerous forbs and graminoids.

There is no obvious adaptation to seed dispersal, except for very locally by ballistic means as the stems become stiff and the capsules arrest seeds until moved (or withered).

There is nothing similar in the Svalbard flora.

Heath vegetation, usually with a mixture of ericaceous plants and forbs and with stable vegetation with little soil disturbance. The known populations are growing on substrates with circumneutral (Colesdalen) or basic (Ossian Sarsfjellet, Bockfjorden) soil reaction (pH).

Thermophilous. Known from three of the climatically most favourable localities in all of Svalbard, in the central and northern fjord districts of Spitsbergen in the middle arctic tundra zone and the weakly continental section: Colesdalen at Isfjorden (Nordenskiöld Land, found in 1998, see Alsos & Lund 1999), Ossian Sarsfjellet at Kongsfjorden (Haakon VII Land, found in 2003, see Alsos et al. 2004), and the warm springs Trollkjeldene at Bockfjorden (Haakon VII Land, found in 1960, see Rønning 1961). Only a few plants have been found on Ossian Sarsfjellet, whereas there are extensive stands (extensive in terms of individuals, not area) in Colesdalen and at Trollkjeldene. The population at Bockfjorden stretches for more than 200 m along the warm springs and was estimated to more than 100,000 individuals (R. Elven observ. 2009). In Ossian Sars-fjellet nearly the entire population was observed within 2 × 4 m (I.G. Alsos observ. 2007). As first found in Colesdalen, only a small patch of less than 1 m² was seen in 1998 but subsequent investigations in 2003 have revealed 9 separate stands along a 4 km transect (Alsos et al. 2004), and in 2007 the inner part of this transect had a nearly continuous population (Alsos et al. 2007), i.e., several thousands of plants.

The species has an amphi-Atlantic range in the southern arctic and northern boreal zones across the North Atlantic from NE Canada and Greenland to Iceland, Jan Mayen, Svalbard, Fennoscandia and N European Russia.

Euphrasia wettsteinii is genetically variable and with a geographic structure in its variation. Genetically, the three Svalbard stands show different affinities to populations elsewhere (Gussarova et al. 2012). The Colesdalen population is most similar to populations in N European Russia, the Bockfjorden population is most similar to Scandinavian populations, whereas the population in Ossian Sarsfjellet show some similarity in both directions but remains unassigned. All the Svalbard populations were genetically distinct from each other and from all the material included from other areas. This suggests that the species has been present in Svalbard for a long time, probably since the warmer parts of the Postglacial (the Hypsithermal), and that there has been subsequent differentiation after at least three independent immigration events.

The Svalbard plants differ from the mainland Fennoscandian ones in a few features: the presence of a few glands on bracts and calyces, and the near absence of dark blotches on the calyces. They should perhaps be studied more closely as to morphology.

Lang, S., Dees, M.W. & Bockmühl, K. 2007. Life in the Arctic – a struggle for survival? Page 33-54 in Alsos, I.G. Körner, C. & Murray, D.F. Arctic plant ecology: From tundra to polar desert in Svalbard. – UNIS publication series, http://www.unis.no/40_LIBRARY_SERVICES/unis_publication_series.htm

Alsos, I.G. & Lund, L. 1999. Fjelløyentrøst Euphrasia frigida funnet i Colesdalen, Svalbard. – Blyttia 57: 36.

Alsos, I.G., Westergaard, K., Lund, L. & Sandbakk, B.E. 2004. Floraen i Colesdalen, Svalbard. – Blyttia. 62: 142–150.

Engelskjøn, T., Alsos, I.G. & Lund, L. 2003. Twenty of the most thermophilous vascular plant species in Svalbard and their conservation status. – Polar Research 22: 317–339.

Gussarova, G., Alsos, I.G. & Brochmann, C. 2012. Annual plants colonizing the Arctic? Phylogeography and genetic variation in the Euphrasia minima complex (Orobanchaceae). – Taxon 61: 146–160.

Liebst, B. & Schneller, J. 2008. Seed dormancy and germination behaviour in two Euphrasia species (Orobanchaceae) occurring in the Swiss Alps. – Botanical Journal of the Linnaean Society 156: 649–656.

Rønning, O.I. 1961. Some new contributions to the flora of Svalbard. – Norsk Polarinstitutts Skrifter 124: 1–20.