Panarctic Flora

641026-30 The Potentilla uniflora aggregate P. subvahliana, P. uniflora, P. villosa, P. villosula, P. vulcanicola

Geography: Asian (N) - amphi-Pacific/Beringian - North American (N).

Notes: Elven and Murray: The group we circumscribe as the Potentilla uniflora aggregate includes several generally similar taxa, some of them possibly hybridogeneous but (from morphological evidence) not involving species outside the aggregate. The taxa have sympatric to parapateric ranges centered on Beringia and are distinguished by several, non-overlapping characters. In our opinion, treatment as several species is justified. The aggregate is very broadly amphi-Pacific/Beringian, distributed from northern Siberia east to northwestern Greenland and southwards along the coasts and in the mountains on both sides of the North Pacific. Its species are characterized by densely tussocky growth, at the base with dense, persistent socks of marcescent stipules and petioles, in some species and races with whole withered leaves, leaves ternate and more or less 'flabellate' where the leaflets have a few coarse and broadly triangular lobes or teeth (but P. villosa with more numerous and rounded teeth), densely and silky hairy with long, soft, and mostly smooth hairs (yellowish or greyish in some taxa), stems mostly with few or single flowers (but P. villosa with several flowers), and flowers large and showy.

Three species were described in the early 19th century: the Pacific coastal P. villosa Pall. ex Pursh 1814 from Alaska, the arctic-alpine P. uniflora Ledeb. 1815 from southeastern Siberia ("Davuria", but see notes to the type of this name), and the arctic P. vahliana Lehm. 1820 from western Greenland. We transfer P. vahliana to the P. gorodkovii aggregate. Five species have been described more recently: P. vulcanicola Juz. 1955 from Kamtchatka (previously as P. uniflora var. ampla Hultén), P. villosula Jurtz. 1984 from the Chukchi Peninsula and with two subspecies (subsp. villosula and subsp. congesta Jurtz. 1993), P. subvahliana Jurtz. 1984 from Wrangel Island, P. gorodkovii Jurtz. 1984 also from Wrangel Island, and P. subgorodkovii Jurtz. 1993 from northern Alaska. We transfer P. gorodkovii, P. subgorodkovii, and an undescribed P. sp. "Quebec" to the P. gorodkovii aggregate. There may be additional, yet unrecognized member(s) of the group in American Beringia, Cordilleran North America south of the Arctic, and in northeastern North America.

After studying the northwestern North American material in 2006, Murray and Elven agree that the morphological differences reported by Yurtsev and Soják (see, e.g., the keys of Yurtsev 1984b and Soják 2004) largely distinguish between identifiable and geographically consistent species (see Elven and Murray 2008a). The major parts of Soják's and Yurtsev's proposals for this group are therefore now accepted by us but with some modifications.

In a recent molecular phylogeny of Potentilla (Eriksson, Eriksen and Töpel, unpubl.), P. villosa is well distinguished from what there was denoted as P. "uniflora" and rather assigns with a species from Turkey. The analysed material of P. "uniflora" is from Alaska and may belong to the P. gorodkovii aggregate.