Panarctic Flora

641030 Potentilla subvahliana Jurtz.

• Jurtz., Fl. Arct. URSS 9, 1: 319, 194 (1984). Holotype (LE): Russian Far East: Wrangel Island, "in curso medio fl. Gusinaja, ad rivulum Leningradskij", 02. July 1970, leg. P.G. Zhukova and V.V. Petrovsky.

2n= 28 (4x). - Far East (N). - Zhukova and Petrovsky in Yurtsev (1984b, counted on the type); Zhukova and Petrovsky (1985b, nine counts). Only reports published for P. subvahliana have been accepted.

Geography: Amphi-Beringian - North American (N): SIB? RFE ALA CAN GRL.

Notes: Yurtsev, Elven, and Murray: Some important changes have been made concerning the circumscription of Potentilla subvahliana compared with Yurtsev (1984b) and his PAF proposal and comments. He would probably have approved these changes. Elven and Murray have edited Yurtsev's comments together with their current opinion into this joint statement.

Potentilla subvahliana is similar to P. uniflora in leaflets deeply dissected into few, narrowly lanceolate, and acute teeth, bracts and epicalyx segments usually free of tomentum, and nutlets glabrous. It differs in being a true cushion plant with entire leaves being retained for several years, the cushion divided into several 'columns', each usually with a single stem and flower.

Potentilla subvahliana is distributed from West Chukotka (Yurtsev 1984b also indicated a single locality in Taimyr but the voucher material should be re-checked) eastwards throughout Chukotka, Alaska, and arctic Canada to northwestern Greenland. It is sympatric with P. uniflora in parts of Chukotka but replaces it on carbonates and basic siliceous rocks. In northwestern North America, Hultén (1968a) mapped it (as P. vahliana) with a string of localities eastwards from the Bering Strait through the Brooks Range and the northernmost Richardson Mountains to across the Mackenzie River. This only represents a small part of its currently known localities in these regions. It is a common plant in northern and northwestern Alaska south to the Seward Peninsula, the northern Yukon Territory, and throughout non-Beringian arctic Canada.

Yurtsev assigned all the non-Beringian arctic Canadian plants to P. subvahliana, whereas he considered P. vahliana to be restriced to Greenland. This view must be revised. Several characters suggest that P. vahliana is a hybrid species with P. subvahliana and P. nivea as its parents (see below). The plants in west-central Greenland and the nearby parts of Canada (west to the Hudson Bay area) show these features, whereas the plants in northwestern Greenland are inseparable from Canadian, Alaskan, and northeastern Asian P. subvahliana. Therefore, both P. subvahliana and P. vahliana occurs in both northeastern Canada and in western Greenland, but with allopatric ranges.

There may be a taxonomically significant variation within what currently is considered P. subvahliana. The plants in Wrangel Island (incl. the type) conforms to the northern Canadian and northwestern Greenland plants. The majority of plants in Alaska, the Yukon Territory, and perhaps in mainland Chukotka differ from those above in even more columnar tussocks, leaves more narrowly dissected, bracts on the pedicels smaller and narrower, flowers smaller, epicalyx segments narrower, and in being in general less hairy. We suspect that two taxa at some level may be present.