Life span

Perennial, moderately long-lived.

Growth form

Solitary herb with a central root, the main stem a stout, woody, unbranched or branched caudex at ground level, branches densely covered with reddish brown remains of stipules and petioles. Most leaves basal. One or more lateral, prostrate or ascending flowering branches up to 15(20) cm.

Leaf

Leaves alternate. Basal leaves from minute to 10 cm long. Petioles up to 4 cm; stipules lanceolate or ovate, acute, adnate to petiole. Blades 1.2–4.0(6.0) × 0.7–2.0(3.0) cm, oblong in outline, pinnate, subglabrous and greyish green or more often densely pubescent with white, silky hairs. Hairs slightly verrucose (VERY strong lens or microscope). Leaflets 3–7 in (1)2(3) pairs, if more than one at a distinct distance from each other and decreasing in size downwards on the blade, ovate, oblong or obovate in outline, each divided essentially to the mid vein with 2–5 lobes per side, lobes linear or narrowly oblong, subacute, with revolute margins and mostly with prominent hair points at lobe ends.

Inflorescence

Inflorescence a cyme with (1)2–5(9) flowers.

Flower

Pedicels straight, short in flowering stage (to 1 cm), elongating in fruit stage, with or without sparse glands. Flowers radially symmetric, small, up to 1–1.5 cm in diameter, with 5 epicalyx bractlets, sepals, and petals. Hypanthium, epicalyx bractlets and sepals with dense, straight hairs and numerous red sessile glands. Epicalyx bractlets 3.5–4.5 × 1.0–1.8 mm, shorter than sepals, oblong, rounded, obtuse or subacute. Sepals 3–5 × 1.8–2.0 mm, obtuse or subacute. Petals 4–5 × 2–3 mm, 1–1.5 times as long as sepals, ovate, elliptic or obovate, truncate or slightly notched, non-overlapping, pale yellow. Stamens ca. 20. Carpels free, ca. 30–50; styles apical, narrowly conical with many and large papillae at base.

Fruit

Fruit a nutlet, often 30–50 per flower.

Reproduction

Reproduction by seeds, probably sexual; no vegetative reproduction. The rather small flowers are potentially insect pollinated; however, as they are little visible compared with those of other species of the genus, some level of self pollination is assumed. Fruit production seems to be regular. Germinability of nutlets is > 90 % (Alsos et al. 2013). Potentilla pulchella is a tetraploid (2n = 28) species and may be predominantly or exclusively sexual. This is different from the majority of arctic species of Potentilla which are higher polyploids and assumed to be at least facultative agamosperms (asexual seed-set).

There are no special adaptations to dispersal; however, local spread of the nutlets is most probably facilitated by wind, also taken into account the very wind exposed sites the species usually occupies.

Comparison

Potentilla pulchella and P. lyngei are distinguished from the other species of Potentilla in Svalbard by having pinnate leaves (the others have ternate or semi-digitate leaves, i.e., with 3–5 leaflets attached at the same or nearly the same point). Potentilla pulchella and P. lyngei differ in the following characters: In P. pulchella the pedicel is rarely 2 cm, the flowers are smaller (< 1.5 mm in diameter), the petals are smaller and only half as broad as long (4–5 × 2–3 mm), and the leaflets have narrower and more deeply dissected lobes; in P. lyngei the pedicel is long (> 2 cm), the flowers are large (> 1.5 cm in diameter), the petals are large and as broad as long (6–9 × 6–9 mm), and the leaflets have broader and less deeply dissected lobes. The complex currently denoted as P. insularis may be similar to P. pulchella and P. lyngei in pubescence of leaves but differs in having semi-digitate leaves.

Habitat

Most common in open or sparsely vegetated sites with abundant clay or loam, such as exposed fluvial deposits with ridges and terraces. More rarely in gravelly or rocky sites such as scree and outcrops. Never seen in dense vegetation. Usually on fine textured soil with good to moderate drainage, but sometimes also with impeded drainage. Nearly confined to substrates with circumneutral or basic soil reaction (pH). Requires almost no snow protection during winter and is adapted to exposed, wind blown sites. Probably little grazed.

Distribution

Fairly frequent in the middle and northern arctic tundra zones and transgressing slightly into the polar desert zone; most frequent in the clearly and weakly continental sections and rare in the transition section. The main range of Potentilla pulchella in Svalbard is in the inner fjord districts of Spitsbergen, but there are a few vouchered sites on Nordaustlandet and one on Edgeøya. Probably due to its dependence of circumneutral or basic soil, P. pulchella is rare south of Van Mijenfjorden and along the west coast.

The general range is interruptedly circumpolar, nearly confined to the arctic zones and especially the northern ones. The range is nearly continuous in N Greenland and Canada but occurs as much more scattered in N Asia; in Europe perhaps confined to Svalbard.

Comments

Potentilla pulchella is very polymorphic, even in Svalbard, a feature which has resulted in much confusion. The species varies from stunted dwarf plants on dry loam slopes and terraces to tall-grown, much branched plants on scree slopes and in bird cliff meadows, and it also varies from sparsely hairy (and therefore grey-green) to silvery white from dense, soft, long hairs. A major part of previous reports of P. rubricaulis Lehm. and P. pedersenii Rydb. from Svalbard (see, e.g., Rønning 1961, 1964, 1979, and see especially the illustrations) were based on misidentified P. pulchella from screes and other less cold sites, whereas the same authors restricted the name P. pulchella to the small-grown plants in unfavourable sites on moist clay and loam. A molecular study has shown that there is nearly no genetic variation among the plants in different habitats, irrespective of whether they are small-grown and subglabrous or tall-grown and silky (Hansen et al. 2000).

Literature

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.

Hansen, K.T., Elven, R. & Brochmann, C. 2000. Molecules and morphology in concert: tests of some hypothesis in arctic Potentilla (Rosaceae). – American Journal of Botany 87: 1466–1479.

Rønning, O.I. 1961. Some new contributions to the flora of Svalbard. – Norsk Polarinstitutts Skrifter 124. 20 pp.

Rønning, O.I. 1964. Svalbards flora. – Norsk Polarinstitutt, Oslo.

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