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Solitary herb with one flowering stem or small tussocks with up to 10(15) stems. Flowering stems simple, erect, 10– 20 cm tall. Stems and leaves with variable cover of brown villous hairs.
Leaves alternate. Basal leaves sheathing with petioles (1)1.5–3.5(4) cm, 4 times as long as blades. Blades 0.8–1.5 × 1.2–2.0(2.5) cm, pedately to palmately divided with one central segment and two broad lateral segments which are further divided into two main segments. Lobes on large leaves are often incised. Stem leaves sessile, palmate to palmatisect with 3–5 linear lobes.
Single, terminal flowers.
The flowers of Ranunculus and Coptidium apparently have green sepals and yellow or white petals; however, what appears to be the sepals are evolutionary the perianth, i.e., tepals, and what appears to be the petals are stamens transformed into staminodia or ‘honey-leaves’ with a nectary pit on the lower upper side. Below, these two kinds of floral leaves are denoted ‘sepals’ and ‘petals’.
Flowers radially symmetric, 1.5–2.2 cm wide, with 5 ‘sepals’ and ‘petals’. ‘Sepals’ ca. 3–5 × 5 mm, ovate or obovate, with a dense cover of dark brown, villous hairs. ‘Petals’ 7–10 × 6–10 mm, almost twice as long as sepals, suborbicular, bright yellow, with dark veins as dry. Stamens numerous (>30), filaments 2–4 mm long, bright yellow. Receptacle taller than broad, glabrous or with a few dark brown hairs apically. Carpels numerous, free.
The fruits are nutlets, glabrous, with beaks about 1 mm long and straight or variously curved. Head of nutlets round or elongated, 0.5–2 × 0.5–0.8 cm.
Sexual reproduction by seeds; no vegetative reproduction. Flowers and fruits regularly and produces numerous nutlets which germinate to about 50 % (Alsos et al. 2013).
Nutlets are dispersed with animals as they attach to fur with their hooked beaks. Otherwise, probably some dispersal with running water and wind.
The stout native Ranunculus species in Svalbard are R. arcticus, R. nivalis, R. sulphureus, and R. wilanderi. In addition, R. repens, R. acris and R. subborealis are introduced (see these species). Ranuculus suphureus and R. nivalis both have dark brown hairs on the ‘sepals’ whereas R. arcticus and R. wilanderi have white hairs. The strange leaves of R. arcticus and R. wilanderi, with the broad middle lobe and the very narrow lateral lobes, immediately distinguish them from R. nivalis with regularly, deeply lobed leaves, R. sulphureus with broad, shallowly lobed leaves, and from the three introduced species, R. acris and R. subborealis with regularly deeply divided leaves and R. repens with three separate leaflets.
Ranuculus nivalis and R. sulphureus are distinguished by the following characters: In R. nivalis the basal leaves are pedate or palmate in outline, the receptacle is glabrous or with brown hears apically only, and by glabrous nutlets; in R. sulphurous the basal leaves are nearly orbicular in outline with some deep lobes apically only, the receptacle is pubescent with long brown hairs all over, and the nutlets are glabrous or with long brown hairs.
Moist heaths and meadows, base of scree, stony places. Seems restricted to well-drained, often coarse substrates. More or less an indifferent species as concerns soil reaction (pH) but avoids the most basic substrates.
Widespread in the middle and the northern arctic tundra zones, perhaps transgressing slightly into the polar desert zone. From the weakly oceanic to the weakly continental section, absent from the clearly continental section. Locally common on Spitsbergen and with a few records from Edgeøya, Barentsøya, and Nordaustlandet. Distinctly more frequent in areas with circumneutral and acidic bedrock than in those with basic bedrock.
The general range is circumpolar in the arctic zones and in mountains in the boreal zones, in Europe south to S Norway.
Alsos, I.G., Müller, E. & Eidesen, P.B. 2013. Germinating seeds or bulbils in 87 of 113 tested Arctic species indicate potential for ex situ seed bank storage. – Polar Biology 36: 819–830. Doi 10.1007/s00300-013-1307-7.