Mat-forming prostrate dwarf shrub, 10(15) cm tall, densely branched and forming clonal carpets, the largest recorded in Svalbard is 50 × 80 m. Twigs terete; annual twigs light brown or red, older twigs brown with a greyish layer of epidermis cells. Bud scales retained at base of shoots.

Leaves alternate, 5–10 × 2.5–5(6) mm, deciduous, obovate or more rarely rounded with entire margins, bluish green, often with purple margins or entire leaf tinged purplish.

Flowers singly in leaf axils.

Flowers radially symmetric with 5 sepals and petals, on short pedicels 1–10 mm, pendulous. Calyx reduced. Corolla 3–5 × 4–5 mm, fused, bell-shaped with triangular lobes, pink. Stamens 10; anthers with horn-like appendages, opening by pores. Gynoecium of 5 fused carpels with a single style.

Fruit is a blue berry.

Sexual reproduction by seeds, potentially; no efficient vegetative reproduction but clonal growth by layering is the main mode of sustenance in Svalbard (Alsos et al. 2002, 2003). The flowers are adapted to insect pollination but self pollination is possible. Flowers have only been observed in some of the populations, in late July and August. Berries have been observed in Colesdalen but they were not ripe at the beginning of September in two years of study. No germinable seed bank has been found (Alsos et al. 2003). The berries are adapted to dispersal by birds and mammals (endozoochory).

There is no similar species in Svalbard.

The known sites in Svalbard are located on slopes with dense heath vegetation and V. uliginosum dominates within its clones. Usually on well or moderately drained, fine textured or mixed substrates. Probably indifferent as to soil reaction (pH) but nearly all occurrences are in sites with circumneutral or basic substrates. Requires a minimum of snow protection during winter but some of the clones reach over to more exposed environments. Probably little affected by grazing.

Clearly a thermophilous species, confined to the most favourable south- and southwest-facing locations with high insolation rates. Only found in the middle arctic tundra zone and in the clearly and weakly continental sections. Only six locations are known: (1) in Helvetiadalen (Nordenskiöld Land), possibly extirpated due to natural erosion (Alsos et al. 2004); (2) at Pyramiden (Dickson Land), observed in the early 1990s (Möller et al. 1995) but not rediscovered in 1998 or 1999 (I.G. Alsos et al. observ.); (3) in Idodalen (Dickson Land), consisting of only two clones of 120 and 60 m² only separated by 3 m (Alsos et al. 2002); (4) in Colesdalen (Nordenskiöld Land), consisting of one large clone (1360 m²) and two smaller ones (3.2 and 16 m²); (5) at Rusanovodden (Nordenskiöld Land), consisting of small patches spread over an area of 150 × 50 m (Alsos et al. 2004); and (6) in Ringhorndalen (Ny-Friesland), one patch of 13 m² (I.G. Alsos & A.K. Brysting observ. 2010).

The general range of the species is circumpolar in the arctic and boreal zones, partly also in northern temperate zones, and in mountains. Subspecies microphyllum is circumpolar but distinctly arctic–alpine.

The few scattered stands of Vaccinium uliginosum in Svalbard have originated from at least two different source regions: East Greenland and Northwest Russia (Alsos et al. 2007). As ripe fruits are not produced in Svalbard today, they may have immigrated in the Holocene warm period 4000–8000 years ago, when the mean temperature was 1–2°C higher than today (Birks et al. 1994). During the last 2500 years, the climate in Svalbard has been similar as today. Based on isoenzyme analyses, the largest clone is about 1360 m². Assuming an annual shoot increment of 25 mm, as found for V. uliginosum ssp. uliginosum in a subarctic region (Shevtsova et al. 1995), it would take a minimum 830 years for a clone to reach the size of 1360 m². Assuming a much lower growth rate in Svalbard than in the subarctic, the clone may be a remnant from before the last cooling took place 2500 years ago.

The Svalbard plants are diploid with 2n = 24. This is the most common ploidy level in this circumpolar arctic subspecies, whereas the amphi-Atlantic boreal ssp. uliginosum is tetraploid (2n = 48) (Alsos 2003; Eidesen et al. 2007; Elven et al. 2011 with much discussion). The Svalbard plants differ from the North European mainland subspecies by having smaller and more rounded leaves and a more prostrate growth form (Alsos 2003). The morphological distinctions are not absolute but the two subspecies are genetically very distinct (Alsos et al. 2005; Eidesen 2007).

A characteristic of ssp. microphyllum is that dead leaves are retained. This has only been observed in one of the Svalbard stands, but unfortunately this stand (in Helvetiadalen) was not refound during a search in 1998 (Alsos & Lund) and was not included in any genetic analyses.

At a global scale, Vaccinium uliginosum is rather complicated morphologically and genetically and has been described as several species and/or subspecies. The European plants divide on ssp. uliginosum in the boreal and low arctic zones and in some mountains, and ssp. microphyllum in the arctic and in South European mountains (remains to be finally proved for Scandinavia). More variation is found in North America and especially in the Pacific regions where 2–3 additional species have been described (see Elven et al. 2011).

Alsos, I.G. 2003. Conservation biology of the most thermophilous plant species in the Arctic: Genetic variation, recruitment and phylogeography in a changing climate – PhD thesis, Tromsø University Museum, Univ. Tromsø, Tromsø.

Alsos, I.G., Eidesen, P.B., Ehrich, D., Skrede, I., Westergaard, K., Jacobsen, G.H., Landvik, J.Y., Taberlet, P. & Brochmann, C. 2007. Frequent long-distance colonization in the changing Arctic. – Science 316: 1606–1609.

Alsos, I.G., Engelskjøn, T. & Brochmann, C. 2002. Conservation genetics and population history of Betula nana, Vaccinium uliginosum, and Campanula rotundifolia in the arctic archipelago of Svalbard. – Arctic, Antarctic, and Alpine Research 34: 408–418.

Alsos, I.G., Engelskjøn, T., Gielly, L., Taberlet, P. & Brochmann, C. 2005. Impact of ice ages on circumpolar molecular diversity: insight from an ecological key species. – Molecular Ecology 14: 2739–2753.

Alsos, I.G., Spjelkavik, S. & Engelskjøn, T. 2003. Seed bank size and composition of Betula nana, Vaccinium uliginosum, and Campanula rotundifolia habitats in Svalbard and northern Norway. – Canadian Journal of Botany 81: 220–231.

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

Birks, H.H., Paus, A., Svendsen, J.I., Alm, T., Mangerud, J. & Landvik, J.Y. 1994. Late Weichselian environmental change in Norway, including Svalbard. – Journal of Quaternary Science 9: 133–145.

Eidesen, P.B. 2007. Arctic-alpine plants on the move: Individual and comparative phylogeographies reveal responses to climate change – PhD Thesis, National Centre for Biosystematics, Natural History Museum, Univ. Oslo, Oslo.

Eidesen, P.B., Alsos, I.G., Popp, M., Stensrud, Ø., Suda, J. & Brochmann, C. 2007. Nuclear versus plastid data: complex Pleistocene history of a circumpolar key species. – Molecular Ecology 16: 3902–3925.

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

Möller, V.I. & Thannheiser, D. 1995. Eine Vegetationsoase im unteren Mimerdalen am Billefjord, Zentral-Spitzbergen. – Polarforschung 65: 65–70.

Shevtsova, A., Ojala, A., Neuvonene, S., Vieno, M. & Haukioja, E. 1995. Growth and reproduction of dwarf shrubs in a subarctic plant community: annual variation and above-ground interactions with neighbours. – Journal of Ecology 83: 263–275.