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Life span

Perennial, moderately long-lived.

Growth form

Solitary herb with a central root, the main parts of the stem a short, ground-level, branched or unbranched caudex with leaf rosettes at the end of caudex branches, and one or more ascending flowering stems, lateral from basal rosettes, reaching 10–15 cm or more.

Leaf

Leaves alternate, mostly basal. Petioles 0.5–3.0(7.0) cm longer than blade, moderately to densely covered by short, entangled, floccose hairs (floccose = flat and crinkly). Blade 0.9–2.0(2.5) × 0.9–2.0(2.5) cm, with three leaflets. Lower leaf surface white due to a dense pubescence of crispate hairs, main and lateral veins with straight, simple hairs. Upper leaf surface dark green, glabrous or nearly so. Leaflets sessile, oblong in outline, not overlapping, terminal leaflet 0.8–1.5(2.0) × 0.4–0.8(1.0) cm, lateral leaflets 0.5–1.3(1.6) × 0.3–0.7(0.9) cm, margins crenate to shallowly lobed with 3–5 pairs of lobes or teeth. Stem leaves reduced, simple or with 2–3 small leaflets.

Inflorescence

Inflorescence a cyme with 1–5 bracteate flowers. Bracts simple.

Flower

Pedicels 1.5–3.5(7.0) cm. Flowers radially symmetric with 5 epicalyx bractlets, sepals and petals. Hypanthium, epicalyx bractlets and sepals moderately or densely pubescent with long white hairs and red glands. Epicalyx bractlets 4–6 x 0.7–1.0 mm, narrowly elliptical, much narrower than sepals. Sepals 5–7 x 1.6–2.2 mm, triangular. Petals 6–9 x 6–8 mm, 1.5–2 times as long as sepals, obcordate, more or less emarginate, yellow. Stamens numerous. Carpels free. Styles apical, narrowly cylindrical with several distinct papillae at base.

Fruit

Fruit a nutlet, up to 20–30 or more from each flower.

Reproduction

Reproduction by seeds, sexual and asexual (agamospermy); no vegetative reproduction. The flowers are adapted to insect pollination but the plant is facultatively agamospermic, that is, able to form seed both sexually and asexually (without fertilization of the egg cell). However, asexual seed development depends upon pollination for fertilization and development of the endosperm (the nutrient tissue for ovule development), a phenomenon named pseudogamy (Müntzing 1928; Gentscheff & Gustafsson 1940). Such endosperm fertilization is often more efficient with pollen from a relative than from the same species (Asker & Jerling 1992; Nyléhn 2002). This makes for interesting possibilities in plants with a potential for hybridization (see Elven et al. 2011). Investigated Svalbard populations of P. nivea are largely agamospermic (Nyléhn 2002). Fruit production is regularly observed in Svalbard (R. Elven observ.).

There are no special adaptations to dispersal.

Comparison

Potentilla arenosa ssp. chamissonis, P. nivea, and what currently is named P. insularis, are the plants of Potentilla in Svalbard that combine the two characters of leaves with 3(5) leaflets attached at the same or nearly the same point (digitate or semi-digitate), and lower leaf surface white pubescent. Potentilla nivea differs from the two others in petioles with exclusively, or at least a total dominance of, floccose hairs (flat, crinkly, and intertwined); the others lack floccose hairs altogether. Potentilla arenosa ssp. chamissonis has long, stiff, often patent, verrucose hairs on the petioles and regularly three leaflets, whereas P. insularis mostly have a denser layer of subappressed, indistinctly verrucose hairs on both petioles and blades and nearly always at least some leaves with more than three leaflets.

Potentilla pulchella and P. lyngei are also often white-pubescent but are distinguished by having pinnate leaves, with two or more pairs of lateral leaflets at some distance from each other. Potentilla crantzii and P. hyparctica also have digitate leaves with 3(5) leaflets but do not have the white pubescence on the lower leaf surface.

Habitat

Almost confined to cliff ledges, rocky outcrops and scree in slopes with high insolation rates, but also observed (albeit rarely) in dry gravelly or stony meadows and heaths. On well-drained, mixed or coarse substrates with circumneutral or basic soil reaction (pH). Requires moderate snow protection during winter but only occurs in sites where the soil is relatively early exposed in spring. Probably little grazed by reindeer or geese.

Distribution

Thermophilous. Confined to the middle arctic tundra zone. Found in the clearly and weakly continental sections, rarely transgressing into the transitional section. Restricted to the inner and middle parts of the fjords of Spitsbergen from Van Mijenfjorden north to Wijdefjorden, Liefdefjorden and Krossfjorden.

The general range is nearly circumpolar and arctic–alpine; however, see Comments for variation.

Comments

Potentilla nivea belongs to a very complicated group – section Niveae – with several species in the circumpolar areas (Soják 1989) and at least two in Svalbard. Some of the species currently included in sect. Rubricaules (with semi-digitate leaves) may also have to be moved to sect. Niveae, among them the Svalbard endemic P. insularis.

The Svalbard plants of P. nivea have previously been assigned to a ssp. subquinata (e.g., by Rønning 1979, 1996) but have been compared genetically and morphologically with the mainland Scandinavian plants (including the type of the name P. nivea) and have been found identical or nearly identical to these. The name P. nivea s. str. is therefore the relevant one for the Svalbard plants. The name P. subquinata is inappropriate in any case; it is based on a type from Greenland, and the type specimen (in Copenhagen, C) shows features from both P. nivea and P. arenosa ssp. chamissonis and is almost certainly a hybrid plant.

However, there is much morphological and probably genetic variation within P. nivea as currently considered (see Elven et al. in Ertter et al. 2014) and there are probably several unrecognized entities (races or even species). The main European entity, to which the Svalbard plants belong, is perhaps restricted to Europe and W Asia. A second entity is recorded from NE Canada, Greenland (Elven in Aiken et al. 2007) and the coastal mountains of Nordland in N Norway (Nyléhn 2002, data from morphology and molecular markers. A third entity is recorded from NW Canada, Alaska, and Chukotka in NE Asia (Murray & Elven 2007). In the future, we may have to accept several subspecies of P. nivea but the Svalbard plant will probably still belong to the type subspecies (ssp. nivea).

Unambiguous hybrids P. arenosa × P. nivea have been collected from at least 5 sites in the Isfjorden and Liefdefjorden districts, usually in the company of both its parents.

Literature

Aiken, S.G. (ed.), Dallwitz, M.J., Consaul, L.L., McJannet, C.L., Boles, R.L., Argus, G.W., Gillett, J.M., Scott, P.J., Elven, R., LeBlanc, M.C., Gillespie, L.J., Brysting, A.K., Solstad, H. & Harris, J.G. 2007. Flora of the Canadian Arctic Archipelago: descriptions, illustrations, identification, and information retrieval. – [CD-ROM version] National Research Council Canada, Ottawa.

Asker, S. & Jerling, L. 1992. Apomixis in plants. – CRC Press, Boca Raton.

Eriksen. B., Jonsell, B. & Nilsson, Ö. 1999a. (1394) Proposal to conserve the name Potentilla nivea (Rosaceae) with a conserved type. – Taxon 48: 165–166.

Ertter, B., Elven, R., Reveal, J.L. & Murray, D.F. 2014 (2015). Potentilla Linnaeus. – In: Flora of North America Editorial Committee (eds.), Flora of North America north of Mexico. 9. Magnoliophyta: Picramniaceae to Rosaceae: 121–218.

Hultén, E. 1945. Studies in the Potentilla nivea group. – Botaniska Notiser 1945: 127–148.

Kurtto, A., Lampinen, R. & Junikka, L. 2004. Atlas florae europaeae. Distribution of vascular plants in Europe. 14. Rosaceae (Spiraea to Fragaria, excl. Rubus). – The Committee for Mapping the Flora of Europe and Societas Biologica Fennica Vanamo, Helsinki.

Müntzing, A. 1928. Pseudogamie in der Gattung Potentilla. – Hereditas (Lund) 11: 267–283.

Murray, D.F. & Elven, R. 2007. A new species and two new combinations in Potentilla sect. Niveae (Rosaceae). – Journal of the Botanical Research Institute of Texas 1: 811–814.

Nyléhn, J. 2002. Predominant cross pollination in an alpine population of the facultative apomict, Potentilla crantzii (Crantz) G.Beck ex Fritsch, Rosaceae. – In: Nyléhn's Dr. scient. Thesis, Univ. Oslo, Oslo.

Rønning, O.I. 1979. Svalbards flora. Ed. 2. – Norsk Polarinstitutt, Oslo.

Rønning, O.I. 1996. Svalbards flora. Ed. 3. – Norsk Polarinstitutt, Oslo.

Soják, J. 1989. Notes on Potentilla (Rosaceae). VIII. P. nivea L. agg. – Candollea 44: 741–762.