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Solitary herb with single stems or small tussocks with usually 1–3 erect or decumbent flowering stems, 3–5(10) cm tall. Flowering stems simple or branched once, as long as or slightly longer than the leaves. Stems and leaves with a sparse but variable pubescence of white hairs.
Leaves alternate. Basal leaves sheathing, with petiole 1–3 cm long; blades 0.5–1.5 × 1–1.5(2.5) cm, about as broad as long or broader, pedately to palmately divided with 3 or 5 lobes, the mid lobe somewhat broader than the side lobes. Stem leaves sessile, palmatisect with 3(5) linear lobes.
Flowers terminal, 1(2).
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, 0.5–0.8 cm wide, with 5 ‘sepals’ and ‘petals’. ‘Sepals’ ca. 3 × 2 mm, ovate or obovate, with sparse or dense, white, villous hairs. ‘Petals’ 1.8–3.0 × 1.0–2.3 mm, as long as or slightly longer than the sepals, oblong, yellow. Stamens 10–15, 1.5–2 mm long, yellow. Receptacle much taller than broad, 4 × 2 mm, glabrous. Carpels numerous, free.
The fruits are nutlets, glabrous, with short beaks about 0.1 mm long and curved about 90°. Head of nutlets elongated, usually 4–6 × 4–5 mm.
Sexual reproduction by seeds; no vegetative reproduction. Flowers regularly and regularly produces numerous ripe nutlets, germinating to ca. 70 % (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 two most small-grown species of Ranunculus in Svalbard – R. hyperboreus and R. pygmaeus – are often confused. They are easily distinguished by R. hyperboreus having 3 ‘sepals’ and ‘petals’ and a prostrate growth form with rooting shoots, whereas R. pygmaeus has 5 ‘sepals’ and ‘petals’ and grows as solitary plants with no rooting shoots. They also differ ecologically: Ranunculus hyperboreus is the perhaps only true aquatic vascular plant in Spitsbergen, whereas R. pygmaeus is confined to dry or only occasionally moist ground.
Tall-grown plants of R. pygmaeus may be confused with small plants of R. nivalis. Ranunculus pygmaeus has smaller flowers (0.5–0.8 cm wide), smaller heads of nutlets (4–6 × 4–5 mm), and the nutlets are much smaller; R. nivalis has larger flowers (1.5–2.2 cm wide), larger heads of nutlets (5–20 × 5–8 mm), and much larger nutlets.
Snowbeds, base of soil slopes, snow protected meadows, and depressions in heaths, base of bird cliff meadows. Mainly on well-drained and often coarse substrates (coarse sand to stones), but often moist or close to brooks. Indifferent as to soil reaction (pH) or perhaps slightly preferring circumneutral to acidic soils.
Distributed in all zones and sections, and common except for the polar desert zone where it is more sparse. Distributed on all major islands in the Spitsbergen group and also common on Bjørnøya.
The general range is circumpolar, mainly in the arctic zones and in mountains in the boreal zones. The species has, however, an extensive range southwards in the Rocky Mountains and isolated in quite southern mountains in E Asia (approaching the Himalayas) and in Europe. These isolated southern outposts are considered glacial relicts. For a phylogeographic study of its immigration in Europe, see Schönswetter et al. (2006).
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.
Schönswetter, P., Popp, M. & Brochmann, C. 2006. Rare arctic-alpine plants of the European Alps have different immigration histories: the snow bed species Minuartia biflora and Ranunculus pygmaeus. – Molecular Ecology 15: 709–720.