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Mat-forming herb with short caudex but extensive stolons from base of flowering stems or from leaf axils. Stolons often 20–40 cm, with nodes at 5–10 cm distance, potentially rooting at every node and with large leaves from all nodes. Stems ascending, up to 20(25) cm. Stolons and stems glabrous or sparsely pubescent (in Svalbard).
Leaves alternate. Basal leaves in a rosette. Petioles 5–10 cm with broad sheaths half clasping the stem, glabrous or sparsely pubescent. Blades up to 5 × 5 cm, sparsely pubescent or glabrous, green, ternately divided (with 3 leaflets on distinct stalks or petiolules), stalks 2–12 mm, much longer on the terminal leaflet than on the lateral ones. Terminal leaflet deeply divided into 3 main segments, sometimes to the base and with stalked secondary segments; lateral leaflets deeply divided into 2–3 main segments. Stem leaves simpler, with more narrow lobes (often 3).
Inflorescence usually a single flower, rarely a small cyme with 2–3 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, up to 15–20 mm in diameter, with 5 'sepals' and 'petals'. 'Sepals' 4–6 × 2–3 mm, reflexed, oblong, obtuse, glabrous, pale brownish yellow. 'Petals' 6–8 × 6–8 mm, broadly obovate, rounded at apex, strongly overlapping, shiny yellow. Stamens numerous, ca. 5 mm; filaments ca. 4 mm; anthers ca. 1 mm, yellow. Receptacle tap-formed. Gynoecium of numerous small, free, green carpels with a hooked style.
Fruit a nutlet (one seed). Nutlets forming a nearly globular head of 15–30 fruits. Fruits not observed in Svalbard.
Sexual reproduction by seeds, probably not realized in Svalbard; local vegetative reproduction by stolons very efficient and may potentially establish extensive stands. Insect pollinated, but some self pollination may occur (stamens and stigmas sit very close together). Fruits not ripe even in late August; probably no fruit-set.
The nutlets, when ripe, are spread by anomals (and people) as they attach easily to fur and footwear due to their hooked styles.
Ranunculus repens and the other introduced species of Ranunculus, R. acris and R. subborealis, differ from the native, yellow-flowered species of Ranunculus in being much taller and usually more or less pubescent on stems, petioles and blades (the others are glabrous). Ranunculus repens differs from all others in its coarse stolons and tripartite leaves with stalked (petiolulate) leaflets, from R. acris and R. subborealis in addition in its usually single flowers with overlapping 'petals' (vs. usually several flowers and contiguous 'petals') and reflexed ‘sepals’ (vs. more or less appressed).
Ruderal ground within settlements, usually on quite coarse, well-drained substrates.
Introduced. Ranunculus repens is recorded from two settlements, from Longyearbyen in 1939 (vegetative) and 2011 (in bud), both probably ephemeral occurrences, and from Barentsburg in 1988 (vegetative), 1993 (vegetative), 2007 (no information), and 2008 (flowering), both sites in Nordenskiöld Land. It may be the same stand that has been observed through the entire period in Barentsburg where it seems to be established vegetatively, even if not reproducing by seeds (yet).
The general range is Eurasian, from the Atlantic east to the Pacific. It is introduced and widespread in North America and also many places in the southern hemisphere.