Solitary herb 2–5 cm tall with one flowering stem, occasionally small tussocks with 2–7 stems. Leaves basal and on the stems. Flowering stems simple or branched once, 4–5 cm and ascending. Stems and leaves mostly glabrous but brown villous hairs common on leaf sheaths and lower surface of leaves.
Leaves alternate. Basal leaves numerous, sheathing, long-stalked with petiole 1–4(4.5) cm, about as long as the blade. Blades 1.0–1.5(1.7) × 1.8–2.5(3.0) cm, all palmatisect with three main lobes which are further incised, apices obtuse. Stem leaves sessile, sheathing.
A single terminal flowers or two flowers in a cyme.
Flowers 1.5–2(2.5) cm wide, radially symmetric with 5 sepals and petals. Sepals 4–5 × 7–8 mm, ovate or obovate, purple, with a dense cover of brown villous hairs. Petals (7)9–12(15) × 10–14 mm, about 1.5 times as long as sepals, broadly overlapping, plicate, initially white but after pollination turning purple. Stamens numerous (>50), bright yellow; filaments 3–4 mm long. Receptacle up to ca. 4 mm, taller than broad, glabrous. Carpels numerous, free, green to purple.
The fruits are nutlets, glabrous and strongly compressed. Beak almost straight or curved. Head of nutlets round.
Sexual reproduction by seeds; no vegetative reproduction. The flowers are adapted to insect pollination; the colour change from white to purple is assumed to be a signal to insects that there is nothing more to collect. No records of seed set or germination, however, based on the large populations in Sørkapp Land (> 300 individuals counted, population size estimated to be about twice as large) the species is assumed to reproduce regularly in Svalbard.
No special adaptations to seed dispersal.
Ranuculus glacialis is rather easily distinguished from all other species of Ranuculus in Svalbard based on the flower colour. Non-flowering plants may be recognized by the palmatisect leaf blades with three lobes that are further incised and with obtuse lobe apices. The two only other species it can be confused with have orbicular leaves with deeply dentate margin (R. suphureus) or blades pedate or palmate with one central segment and two broad lateral segments which are further divided into two main segments (R. nivalis).
Ranunculus glacialis is usually found on moist, well drained, acidic substrates. Vegetation analyses from the stands at Sørkapp Land revealed a wide ranges of stone and moss cover (0–80 and 10–80 % respectively), whereas the cover of vascular plants was low (5–30 %). The soil was moist and had a pH of 5.8–5.9 (Alsos and AB-201 students 2008, unpublished).
Only documented from four places at the south tip and southwest coast of Spitsbergen in Sørkapp Land and Wedel Jarlsberg Land (1 place) and from an imprecisely given locality on W Nordenskiöld Land (“between Bell Sound and Ice Fjord”, 1882, M. Jakobsen, TROM). Only found in the northern arctic tundra zone and the weakly oceanic section.
Ranunculus glacialis s. str. is amphi-Atlantic and arctic–alpine, restricted to E Greenland, the North Atlantic islands from the Faeroes and Iceland north to Svalbard, Fennoscandia, and the mountains of C and S Europe. A vicariant plant is found in Seward Peninsula by the Bering Straits in Alaska (see Comments).
There are two disjunct subspecies: the amphi-Atlantic ssp. glacialis and the amphi-Beringian ssp. alaskensis (Yurtsev et al. 2012). The populations in Svalbard belong to ssp. glacialis which are elsewhere found in Greenland, Iceland, Scandinavia, NW Russia, and the more southern mountains of Europe. Whereas there is high genetic variation in C European populations, there is little genetic variation and no phylogeographic structure in populations in N Europe and Greenland (Schönswetter et al. 2003). A critical evaluation of the Atlantic–Beringian paradox is given by Ronikier et al. (2012).
Ronikier, M., Schneeweiss, G.M. & Schönswetter, P. 2012. The extreme disjunction between Beringia and Europe in Ranunculus glacialis s.l. (Ranunculaceae) does not coincide with the deepest genetic split – a story of the importance of temperate mountain ranges in arctic–alpine phylogeography. – Molecular Ecology 21: 5561–5578.
Schönswetter, P., Paun, O., Tribsch, A. & Niklfeld, H. 2003. Out of the Alps: colonization of Northern Europe by East Alpine populations of the Glacier Buttercup Ranunculus glacialis L. (Ranunculaceae). – Molecular Ecology 12: 3373–3381.
Yurtsev, B.A., Murray, D.F. & Elven, R. 2012. Ranunculus glacialis subsp. alaskensis subsp. nov. (Ranunculaceae), a Beringian race of an otherwise Atlantic species. – Journal of the Botanical Research Institute of Texas 6: 17–24.