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Weakly mat-forming herb with a short, more or less erectrhizome. Cauxed unbranched or sometimes branched, covered with black remains of petioles and sheaths, often disintegrating into fibres. Leaves in a basal rosette and on stems. Stems erect, 2–3 mm broad at base, up to 20 cm (Svalbard) or 45 cm (Bjørnøya) long, branched in the upper part, slightly ridged, glabrous or with sparse, coarse, patent, yellowish hairs.
Leaves alternate. Basal leaves in a rosette. Petioles 3–5 cm with broad sheaths half clasping the stem, densely pubescent with coarse patent yellowish hairs up to 1–1.5 mm long. Blades up to 4 × 4 cm, divided to 3/4 or more towards the base (palmatifid) into usually 3 primary segments, each divided again for 1/3–2/3 into 3 broadly cuneate secondary segments with fairly broad, obtuse or subacute lobes and teeth, evenly pubescent with subappressed, yellowish hairs, green. Stem leaves simpler with more narrow lobes (often 3).
Inflorescence an irregular cyme with 1–5(7) flowers, bracteate and with small bracteoles on pedicels, densely pubescent with subappressed hairs.
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’.
Pedicels terete, up to 4–5 cm. Flowers radially symmetric, up to 2.0 cm in diameter, with 5 'sepals' and 'petals'. 'Sepals' 3.5–4.5 × 1.8–2.3 mm, more or less appressed to 'petals', elliptic or oblong, obtuse, more or less densely pubescent with white, subappressed hairs, yellowish green or purplish at apex. 'Petals' 9–11 × 7–9 mm, obovate, rounded at apex, contiguous (margins touching the neighbour petals but not overlapping), shiny yellow. Stamens numerous, ca. 5 mm; filaments ca. 4 mm; anthers ca. 1 mm, yellow. Receptacle tap-shaped. Gynoecium of numerous small, free carpels with a hooked style.
Fruit a nutlet (one seed). Nutlets forming a nearly globular head of 15–30 fruits. No fruits observed in Svalbard.
Sexual reproduction by seeds, probably not reproducing in Svalbard; possibly some very local vegetative reproduction by disintregration of old rhizomes. 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 dispersed by animals (and people) as they attach easily to fur and footwear due to the hooked style.
Ranunculus acris and the other introduced species of Ranunculus, R. repens and R. subborealis, differ from the native, yellow-flowered species of Ranunculus by 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'). Ranunculus acris and R. subborealis are best separated by the pubescence of stems and petioles, appressed and white in R. acris, patent, coarse and yellowish in R. subborealis. The basal leaves of R. acris usually have 5 primary segments and acute terminal segments, those of R. subborealis ssp. villosus usually 3 primary segments and subacute to obtuse terminal segments (the segments are acute in ssp. subborealis, see below).
Ruderal ground within settlements, usually on fairly coarse, well-drained substrates.
Introduced. Ranunculus subborealis has been recorded from three settlements on Svalbard and by two cabins on Bjørnøya, but seems to have (or have had) a stable presence only on Bjørnøya where it has been observed at Tunheim in four years from 1957 to 1967. The other Bjørnøya locality is at Krillvatnet where it was found flowering in 1957. As this is a perennial species that does not reach flowering stage in the Arctic in its first years, it has been present both at Krillvatnet and at Tunheim for several years before being first found. On Spitsbergen, it has been recorded eight times but does not seem to have had any long-lasting stands: Hotellneset in 1928 (vegetative), Longyearbyen in 1928 (vegetative), 1939 (flowering) and 1960 (flowering), and Ny-Ålesund in 1928 (vegetative), 1936 (flowering) and 1958 (flowering in two places).
The general range of ssp. villosus is North Atlantic in Britain, the Faeroes, Iceland and W Scandinavia, with ssp. subboreralis replacing the former eastwards in NE Fennoscandia, N European Russia and NW Siberia (see Elven et al. 2011).
Ranunculus subborealis is disputed as a species apart from R. acris. Arguments in its favour are found in Elven et al. (2011, 2013). It seems to be a northern counterpart to R. acris with little if any transitional forms towards that species. In N Europe, it replaces R. acris in Iceland, the Faeroes, the northern parts of Britain, and in the major parts of W, C and N Norway, possibly in three races. Subspecies villosus is the major race of Norway (and the northern British Isles, the Faeroes, and Iceland) and reaches north to NE Troms, being replaced by ssp. subborealis in Finnmark and eastwards in Russia to NW Siberia, and by ssp. pumilus in the high mountains of Scandinavia and Iceland. It is no surprise that this is the taxon of the R. acris group most often found in the Norwegian settlements. The two major Norwegian ports for supplying Svalbard have traditionally been Tromsø and Bergen, the latter due to the major Norwegian coal company earlier having its major shareholder and main office in Bergen. Both Bergen and Tromsø are located in regions where R. subborealis ssp. villosus is the almost exclusive taxon of the group.
Elven, R., Fremstad, E. & Pedersen, O. (eds.) 2013. Distribution maps of Norwegian vascular plants. IV The eastern and northeastern elements. – Akademika Publishing, Trondheim.
Elven, R., Murray, D.F., Razzhivin, V. & Yurtsev, B.A. (eds.) 2011. Annotated Checklist of the Panarctic Flora (PAF).