Panarctic Flora

641035-39 The Potentilla nivea aggregate P. arenosa, P. crebridens, P. drymeja, P. nivea, P. prostrata

Geography: Circumpolar-alpine.

Notes: Yurtsev, Elven, and Murray: The basic morphological study of the Potentilla nivea aggregate is Soják (1989). Elven and Murray (2008c) surveyed the variation in northwestern North America. We have reached a solution close to consensus in this aggregate and Elven and Murray have edited a joint statement. The points that still are debated are commented on below.

Leaves are predominantly ternate with lateral leaflets sessile and terminal leaflet sessile to short-stalked. Flowers are intermediate-sized, larger than in P. pulchella and relatives, smaller than in the P. uniflora and the P. gorodkovii aggregates. The main differences within the aggregate are found in the hairs.

Two of the species of the P. nivea aggregate are characterized by a dense pubescence of floccose (flat, crinkly) hairs and absence of straight, verrucose hairs on petioles and often on stems. Upper leaf surfaces are glabrous, subglabrous, or with a dense cover of short, often crispate hairs, whereas lower leaf surfaces are white from dense crispate hairs, often mixed with long straight hairs. Crispate hairs may also occur but do never dominate on petioles and stems. We accept two species: P. crebridens with the amphi-Beringian subsp. hemicryophila, and the widespread P. nivea possibly with two or more races (not yet circumscribed and named). These two species are fairly uniform, fairly well distinguished from P. arenosa s. lat., and circumpolar and arctic-alpine.

Plants with petioles without floccose hairs but with either only long verrucose hairs or a combination of these and short (non-floccose) hairs are assigned to P. arenosa with two subspecies.

Plants with petioles with a combination of long verrucose and short floccose hairs are considered as hybrids or hybrid species between P. arenosa and P. nivea or P. crebridens and are entered as two hybrid species: P. drymeja and P. prostrata.