Mat-forming herb with extensive (subterranean or floating) branched stems (rhizomes), very stout and white, rooting at the nodes, and with erect, stalked leaves and flowers from the nodes. Lateral shoots developing from axial buds within the leaf sheaths. Stems and leaves glabrous.

Leaves alternate. Petioles usually (5)10–14(20) cm long and 2–5 mm broad. Blades 1.5–3.0 × 0.4–1.2 cm, linear to oblong in outline, either entire or dissected for 20–50(70) % of the blade with one broad mid lobe and one or two smaller lateral lobes reaching about 2/3 the length of the mid lobe.

Single terminal flowers on pedicels 2–10 cm, usually shorter than the leaves.

Flower radially symmetric, 1.5–2 cm wide, with 3 ‘sepals’ and 6–10 ‘petals’. ‘Sepals’ 6–7 × 5–6 mm, shorter than ‘petals’, not deflexed, broadly ovate in outline, almost as broad as long, outer surface purple and inner surface white or purple. ‘Petals’ 7–10 × 5–6 mm, narrowly obovate with an uneven apex, white. Stamens numerous (>20), ca. 4 mm, with yellow anthers and greenish yellow filaments. Receptacle up to 3 mm long, glabrous. Carpels numerous, free, yellowish green with purple.

The fruits are nutlets, glabrous, only slightly compressed, and with short, straight beaks. Head of nutlets globose.

Reproduces sexually by seeds; efficient local vegetative reproduction due to growth by rhizome and fragmentation. Pollinated by insects but it is not known whether it is selfing or outcrossing (Brochmann & Steen 1999). However, the strong fragrance of the flowers suggests insect pollination. The plant flowers regularly at least at some localities and produces numerous nutlets. No germination was observed in 140 seeds collected 4. Sept. 2008 but nutlets are assumed to ripen in good summers (Alsos et al. 2013). Lack of germination may also be due to some special handling needed for getting rid of inhibitors in the seed coat.

The nutlets have a floating tissue and dispersal is assumed to be mainly by water and by birds (internal and external). We assume some dispersal of detached shoot fragments by water or birds.

The species of the genus Coptidium differ from those of the genus Ranunculus in several features, the most evident being the thick, white underground or under-water stems (rhizomes) and the leaves and flowers arising mostly singly from these stems. There is nothing similar in Ranunculus. Another difference is the fragrant flowers of Coptidium (no fragrance in Ranunculus). Less visible is the corky floating tissue in the fruits of Coptidium, absent in Ranunculus.

Coptidium pallasii and C. spitsbergense are both aquatic and have similar growth form. Flowering plants are easily distinguished as C. pallasii has white and much larger flowers than C. spitsbergense with comparatively small, pale yellow flowers. Non-flowering plants are distinguished by the blade: In C. pallasii the blade is entire or dissected for 20–50(70) % of its length into one broad mid lobe and 1–2 smaller lateral lobes reaching about 2/3 the length of the mid lobe; in C. spitsbergense the blade is dissected for (50)60–80 % and the lateral lobes often dissected again.

Helophyte or hydrophyte. Growing in wet moss tundra or on mud in shallow ponds. Vegetation analyses of one population at Bohemanflya revealed a high moss cover (80–100 %), low cover of vascular plants (1–30 %), no stone or bare ground, and low cover of cryptogamic crust in some plots, and very wet conditions with slow-moving water. The pH was 6.5 (Alsos and AB-201 students 2008, unpublished).

Thermophilous. Only found at 6 localities in Spitsbergen, all within the middle arctic tundra zone and the weakly continental section, in Reindalen and the Adventdalen area (Nordenskiöld Land) and at Bohemanneset (Oscar II Land). The Svalbard populations are the only ones in NW Europe (the species is known from easternmost Kola Peninsula in Russia) and by far the northernmost ones known in the world.

The general range is nearly circumpolar in the southern arctic and northern boreal zones, but with a gap over Greenland and most parts of N Europe.

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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.

Brochmann, C. & Steen, S.W. 1999. Sex and genes in the flora of Svalbard - implications for conservation biology and climate change. – Det Norske Videnskaps-Akademi. I. Matematisk Naturvitenskapelig Klasse, Skrifter, Ny serie 38: 33–72.