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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 lateral, ascending flowering stems reaching 10–20 cm or more. Flowering stems lateral on basal rosettes.

Leaf

Leaves alternate, mostly basal, with long petioles and ternate with three leaflets. Petiole (1.5)2–5.5(7.5) cm, longer than blade, sparsely covered by long, straight, verrucose hairs (a VERY strong lens is needed to see that they are verrucose, preferably a microscope), sometimes mixed with short, crispate hairs, but never with floccose hairs (see Comparisonfor explanation of ‘floccose’). Blade (2)2.5–3.5(4) × (2)2.5–4 cm. Lower leaf surface white due to dense pubescence of crispate hairs, main and lateral veins with straight, simple hairs. Upper leaf surface dark green, subglabrous or with long, straight hairs. The two lateral leaflets sessile, (1.0)1.2–2.5(2.8) × 1–1.5(2) cm, the terminal with a short stalk (petiolule) or narrowly cuneate towards base, (1.5)1.8–3.0(3.5) × (1.0)1.2–2.0 cm. Leaflets oblong in outline, non-overlapping, dentate or 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 a few (1–5), bracteate flowers. Bracts simple.

Flower

Pedicels long, (3)4–6(7) cm. Flowers radially symmetric with 5 epicalyx bractlets, sepals and petals. Epicalyx bractlets 3–4 x 0.5–1.2 mm, narrowly elliptic, narrower than the sepals. Sepals 4–5 x 2–3 mm, narrowly triangular. Petals 6–10 x 6–9 mm, 1.5–2 times the length of sepals, obcordate, more or less emarginate, yellow. Stamens numerous. Carpels free, numerous. Styles apical with several distinct papillae at base.

Fruit

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

Reproduction

Reproduction by seeds, probably both 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. arenosa ssp. chamissonis are largely agamospermic (Nyléhn 2002). Fruit maturation is quite regular in Svalbard (R. Elven observ.).

There is no special adaptation 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 much insolation, but also observed (albeit rarely) in dry gravelly or stony heath or on loamy plains. On well drained, mixed, or coarse substrates with neutral 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. In the middle arctic tundra zone and in the clearly and weakly continental sections, rarely transgressing into the transitional section. Restricted to Spitsbergen where there are several sites along the inner and middle parts of Isfjorden and Wijdefjorden and a very few at Kongsfjorden and Krossfjorden.

The general range is amphi-Atlantic; see Comments.

Comments

Potentilla arenosa is now accepted as name for a circumpolar species of section Niveae (Murray & Elven 2007; Elven & Murray in Ertter et al. 2014). Two main races are recognized: ssp. chamissonis is broadly amphi-Atlantic and has petioles only or mainly with long, straight hairs; ssp. arenosa is Siberian, amphi-Beringian, and North American to Greenlandic and has in addition a lower layer of short, stiff bristles under the long petiole hairs. An unresolved var. nipharga (Rydb.) (P. nipharga Rydb.; P. nivea var. nipharga (Rydb.) Soják) in Canada and Greenland has the short bristles replaced by short curved hairs. The genetic background of this variation is not known. Subspecies chamissonis, in our current concept, is present in NE Canada, the southern half of Greenland, Svalbard, Fennoscandia, and in Russia perhaps eastwards to the Urals. Russian botanists (and Kurtto et al. 2004) have applied the name P. kuznetsovii (Govor.) Juz. to the Russian plants but this name is without a type (as far as we know) and therefore without a current meaning until a neotype is selected.

In more recent times, the name P. hookeriana Lehm. has sometimes been applied to the Svalbard plant. This name is currently connected to a more local species in the Rocky Mountains (Ertter et al. 2014) and is not available for the circumpolar species. However, the combination P. hookeriana ssp. chamissonis refers to the plants in Svalbard.

Hultén (1945) did a mistake when first describing the species P. chamissonis. He assigned one of the two Linnaean specimens annotated as P. nivea as a type for his new species P. chamissonis, whereas he assumed the other specimen to belong to the (floccose) P. nivea. It does not; it belongs to the Siberian P. arenosa s. str. as shown by Soják (1989). Eriksen et al. (1999) rectified this mistake by designating a new type for the name P. nivea, making this name the valid one for the plant with floccose hairs on the petioles.

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

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

Eriksen. B., Jonsell, B. & Nilsson, Ö. 1999. (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: J. Nyléhn's Dr. scient. Thesis, Univ. Oslo, Oslo.

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