Life span

Perennial, probably very long-lived.

Growth form

Mat-forming herb with very extensive branched rhizome system with horizontal branch lengths of 2–10 cm between vertical branches ending in aerial shoots. Aerial shoots 3–5(6) cm, erect, at base with several ovate, pale brown, glabrous prophylls (sheaths only). Stem leaves 1–2. Stems reddish with short stipitate pale brown glands and very thin hairs, 0.3–0.7 mm, white and retrorse (downwards pointing).

Leaf

Leaves alternate. Petioles 4–8 mm, with glands and hairs like stems. Stipules 2–5 x 1.5–2 mm, ovate, glabrous except for glands in the margin. Blades 1.8–2.3 × 2.3–2.7 cm, reniform, rugose, palmately veined with 5 main veins and 5 shallow lobes with crenate margins, dark or reddish green. Veins strongly raised on lower surface, slightly impressed on upper surface (i.e., the rugose appearance). Veins and both surfaces with abundant stipitate glands, lower surface and veins also with short white hairs, upper surface glabrous or with sparse white hairs towards margin.

Inflorescence

Single flowers terminally on aerial shoots.

Flower

Flowers radially symmetric, hypogynous (perianth at the base of the gynoecium), with no epicalyx bractlets and (4)5(6) free sepals and petals, and with convex receptacle (as a tap in the mature fruit). Dioecious with functionally female and male flowers on different plants (clones). Sepals (5)6–7(8) × 3–4 mm, ovate, the two outer ones often irregularly dentate or lobed at apex, the three inner ones entire, brownish red with white hairs and stipitate glands. Petals (7)8–11(12) × (5)6–7(8) mm, obovate, white. Male flowers with numerous stamens (>20) with slender filaments 2 mm and rounded anthers 0.7 mm, cream, also with some reduced, non-functional carpels. Female flowers with 8–20 (or more) free carpels, ovate or globular, with apical and slender cylindrical styles 1.5–2 mm, also with very small rudiments of stamens.

Fruit

Fruit a head of 1-seeded drupelets (drupelets have a juicy outer fruit wall and a firm inner wall enclosing the single seed), orange when mature, very sweet tasting.

Reproduction

Sexual reproduction by seeds; efficient local vegetative reproduction by extensive growth of rhizomes and fragmentation of such ones. Pollination depends on insects flying between male and female clones. However, the majority of stands in Svalbard are unisexual and the distances between clones usually much too long for cross pollination to take place today. Both sexes are present at Colesbukta (Nordenskiöld Land) and a single mature fruit has been found at Sveaneset (James I Land), strongly indicating presence of both sexes. This fruit was immediately eaten by the finder and not preserved for science.

Fruit dispersal with birds.

Comparison

There is nothing similar to Rubus chamaemorus in Svalbard. The large white flowers are shared by Papaver (in part) and Dryas but the growth forms of these three are entirely different (and Rubus grows in an entirely different habitat from those of the two others).

Habitat

Shallow mires and sloping, wet moss tundra, usually on low hummocks with peat production and very little frost disturbance of the substrate at surface level. Rather indifferent as to soil reaction (pH) but in Svalbard only found on circumneutral to slightly basic substrates.

Distribution

Thermophilous. Restricted to the middle arctic tundra zone and the weakly continental section. The species is only known from some of the climatically most favourable places in Spitsbergen and only found in the Isfjorden districts. A total of 14 stands supposed to be clones are known, in 9 part populations in 6 localities: (1) Colesbukta–Colesdalen (Nordenskiöld Land) where 4 female clones and 2 male clones are present at Rusanovodden and where 10 samples showed 6 genetic individuals (Engelskjøn et al. 2003), and 2 male clones are present in Colesdalen (Alsos et al. 2004). (2) Ekmannfjellet (James I Land) where 2 male clones are present, and (3) Hemsilelva (James I Land) where a female clone is present, totally with three genetic individuals (Ehrich et al. 2008). (4) Sveaneset (James I Land), where the fruit was found. (5) Kapp Thordsen (Dickson Land) with several clones, at least one of these female (observed in 1992). And (6) Sassendalen (Sabine Land), where the plant was last seen in 1913.

The general distribution is circumpolar in the southern arctic and boreal zones, very common in most parts of N Eurasia and North America. The Svalbard localities are by far the northernmost known in the world.

Comments

The interrupted range in Svalbard, with long distances between the four main areas (Colesbukta, Sveaneset–Ekmanfjorden, Kapp Thordsen, Sassendalen) may be explained in two ways: either as remnants of a previously more continuous distribution in the warmer parts of the Postglacial (the Hypsithermal), or due to several independent introductions by bird dispersal from more southern latitudes. We favour the former hypothesis. Genetically, the Svalbard populations are most closely related to populations in Scotland and Scandinavia (Ehrich et al. 2008).

Literature

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

Ehrich, D., Alsos, I.G. & Brochmann, C. 2008. Where did the northern peatland species survive the dry glacials? Cloudberry (Rubus chamaemorus) as an example. – Journal of Biogeography 35: 801–814.

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.