Life span

Perennial, long-lived.

Growth form

Solitary herb with a tuber-like, 7–10(12) mm thick rhizome with erect caudex branches 5–10 mm thick, covered by scaly, pink leaves 3–7 × 3–7 mm. Rhizome smelling of roses when broken of chewed. Aerial stems from the broad ends of caudex branches which are covered with short, scaly leaves, one or several stems from each main caudex branch, 3–8 cm long and 1–1.5 mm thick, slightly succulent, yellowish green or reddish, with leaves up to the inflorescence. The entire plant is glabrous.

Leaf

Leaves alternate, crowded along the stems or concentrated to the distal half, 8–15(20) × 6–10(13) mm, sessile or slightly clasping (amplexicaul), broadly obovate or oblong, succulent, entire, crenate or shallowly dentate, obtuse, with indistinct veins, bluish green or tinged with red, turning intensely purplish red in autumn.

Inflorescence

Inflorescence a single, short and condensed terminal cyme on each stem, 0.5–1.2 × 1–2.5 cm, with 10–30 flowers.

Flower

Plants dioecious (separate male and female plants). Flowers with 4 free sepals and petals. Male flowers with petals ca. 2 × 1 mm, oblong, yellow or more often tinged with red. Stamens 8; filaments 3–4 mm, much exerted from the flower; anthers suborbicular, ca. 0.4 × 0.4 mm. Fairly large but non-functional carpels are found in the male flowers. Female flowers with petals the shape and size of male flowers but usually red. Gynoecium of 4 free carpels. Rudiments of stamens are found in female flowers.

Fruit

Red follicles, each with several seeds.

Reproduction

Sexual reproduction by seeds; no vegetative reproduction. Obligate out-crossing due to the plants being dioecious. Insect pollinated. Seed set in Svalbard not investigated but assumed to be poor and infrequent.

No special adaptations to seed dispersal but the stiff stems and the erect follicles ensure some very restricted ballistic spread.

Comparison

There is nothing similar in the Svalbard flora.

Habitat

On Bjørnøya found mainly on the coastal terraces, directly on mineral soil or in short-grown vegetation carpets, but with little composition. The ecology on Prins Karls Forland is not known. Usually this is a plant of rocks, crevices in stones, and in dry heath with open patches. Probably indifferent as to soil reaction (pH).

Distribution

Thermophilous. Middle arctic tundra zone and weakly oceanic section. On Bjørnøya Engelskjøn & Schweitzer (1970) reported 37 localities, i.e., as rather common. There are reports not yet supported with specimens from somewhere on Prins Karls Forland west of Spitsbergen (not included in map). Rhodiola rosea belongs to a west coast element in Svalbard, with, e.g., Cerastium alpinum, Luzula arcuata, Ranunculus glacialis, and Salix herbacea.

The general range depends somewhat on how the species is circumscribed. In our circumscription (Elven et al. 2011), the range is amphi-Atlantic in NE Canada, Greenland, the North Atlantic islands from Britain northwards to Svalbard, Fennoscandia, and in N European Russia east to the Urals.

Comments

Engelskjøn & Schweitzer (1970) accepted the Bjørnøya plant as a taxon different from Rhodiola rosea s. str.: asssp. arctica (or rather as Sedum rosea ssp. arcticum) "since it differs only quantitatively from the nominatic of the species". The differential characters given by Borisova (1939) are all quantitative and characterize a smaller plant. Korobkov (in Elven et al. 2011) synonymized Rhodiola arctica with R. rosea s. str. Rhodiola arctica (R. rosea ssp. arctica) occurs in the arctic and northern alpine parts of the range of R. rosea, mainly in N Europe. High mountain plants of Fennoscandia are inseparable morphologically from the arctic plants. We have followed the transition from the large-grown plants in the north boreal zone to the high alpine plants (at above 2200 m a.s.l.), and have not seen any discontinuity in the variation pattern. The high alpine plants are inseparable from Borisova's ssp. arctica in all reported features. The transition to R. rosea s. str. is therefore gradual and clinal and does not support recognition of races. We agree that it probably is not appropriate to accept an arctic and high-alpine European race.

Literature

Borisova, A.G. 1939. Crassulaceae DC. – In: Komarov, V.L. (ed.), Flora SSSR 9: 8–134, 471–486.

Elven, R., Murray, D.F., Razzhivin, V. & Yurtsev, B.A. (eds.) 2011. Annotated Checklist of the Panarctic Flora (PAF).

Engelskjøn, T. & Schweitzer, H.J. 1970. Studies on the flora of Bear Island (Bjørnøya). I. Vascular plants. – Astarte 3: 1–36.