Panarctic Flora

641014 Potentilla pedersenii Rydb.

• Rydb., N. Amer. Fl. 22: 332 (1908). Described from Vaigat Assuk on Disko Island (Greenland).
• Potentilla tolmatchevii Jurtz. & Soják, Fl. Arct. URSS 9, 1: 320 (1984). Holotype (LE): Siberia: "in cursu inferiore fl. Jenisei prope pagum Sopocznaja Karga", 12. Aug. 1926, leg. A.I. Tolmatchev.
• Potentilla tolmatchevii var. zubkovii Jurtz. & Soják,
• Fl. Arct. URSS 9, 1: 320 (1984). Holotype (LE): European Russia: Novaya Zemlya, "Pankova zemlja, prope pagum Lagernoje, ad ripam dextram fl. Bezymjannaja", 03. Sept. 1947, leg. A.I. Zubkov.
• Potentilla rubricaulis auct., non Lehm. (1830).

Geography: European (N) - Asian (N) - amphi-Beringian - North American (N): NOR RUS SIB RFE CAN GRL.

Notes: Elven and Murray: Potentilla pedersenii, P. tolmatchevii, and P. tolmatchevii subsp. zubkovii are all interpreted as hybrid offspring from P. arenosa s. lat. and P. pulchella. As such, they should be treated (at best) as a single hybrid species, with nothosubspecies if subspecies of P. arenosa are accepted.

Potentilla pedersenii. - Yurtsev: According to personal communication by Soják, the majority of the material kept in Canadian herbaria as P. rubricaulis belongs to P. pedersenii.

Elven, Aiken, and Murray: We largely agree with Yurtsev's note above. Yurtsev (PAF proposal) interpreted P. pedersenii to be a hybrid species from P. pulchella and a species of sect. Niveae. We find morphological support for that view and consider P. arenosa subsp. arenosa to be the probable parent from sect. Niveae, due to the presence of verrucose hairs and the lack of floccose hairs typical of P. nivea. We accept this name as a priority name for a major and fairly consistent group of populations with semidigitate leaves in Russia, northeastern North America, Greenland, and Svalbard. These plants are sometimes conspicuously rich-flowered with comparatively small flowers (14-16 mm in diameter), a possible influence from P. pulchella. These may be the only plants of this group in eastern and western Greenland and in Ellesmere, Axel Heiberg, and perhaps Devon islands. There is, however, much polymorphy in the very insufficiently studied Greenland and Svalbard material.

Potentilla tolmatchevii. - Elven and Murray: Potentilla tolmatchevii is assumed to be a hybrid species from P. arenosa subsp. arenosa and P. pulchella. This parentage is the same as assumed for the earlier described P. pedersenii. Yurtsev annotated numerous Ellesmere Island specimens (ALA) as P. tolmatchevii (from his knowledge of that plant from Russia), in the central parts of the range of P. pedersenii. We confirm these and they obviously form populations in Ellesmere.

The synonymization of P. tolmatchevii with P. pedersenii depends on how to treat taxa presumed to have developed from hybrids of the same parental combination. In Soják's approach, they should be considered synonymous but Yurtsev considered them as two species, probably due to morphological differences. We have not thoroughly compared North American and Greenlandic material of P. pedersenii with Russian material of P. tolmatchevii but do not see much difference in the samples we have seen. However, the Ellesmere plants assigned by Yurtsev to P. tolmatchevii differ from 'typical' P. pedersenii in, e.g., larger and fewer flowers.

Yurtsev: In the type specimen of [P. tolmatchevii] leaves are partly ternate, partly semidigitate to shortly pinnate which clearly indicates participation of a species from sect. Pensylvanicae. The original combination of characters forces one to consider the plant as a taxon. Most of the characters, though, are in common either with P. arenosa subsp. [arenosa] (general appearance, dissection of leaflets, stiff longer hairs on petiols etc.) or with P. pulchella (semidigitate to shortly pinnate leaves, stiff short hairs in the lower 2/3 of petiole, obovate petals etc.). The lower layer of pubescence in the upper part of petioles is shortly tomentose. The wool on lower side of leaflets is lax, greenish-canescent. The glandulose base of styles is common to both species.

A series from Sopoctznaya Karga may represent a population. A similar plant from the center of Wrangel Island was represented by few individuals and may be primary hybrids.

Elven, Aiken, and Murray: The interrupted Russian range reported by Yurtsev for P. tolmatchevii might indicate a series of polytopic, restricted, probably hybridogeneous biotypes without the sufficient consistency we prefer to have in a species. However, the northeastern Canadian and Greenlandic plant indicated above as P. pedersenii, probably of the same parentage, certainly forms large populations and has a range of its own. It is a major constituent of the Potentilla flora of Arctic Canada and Greenland.

Potentilla tolmatchevii var. zubkovii. - Yurtsev: The collection of [Potentilla tolmatchevii] by A.I. Zubkov from Novaya Zemlya differs in a few characters (including absence of short stiff hairs on the lower part of petioles, the upper part tomentose). Ternate leaves are almost absent. This collection was described as P. tolmatchevii var. zubkovii. Its parentage could be P. arenosa subsp. chamissonis x P. pulchella. If it is proved, the taxon will receive the status as a hybrid species Elven: or nothosubspecies.

Elven: A major part of the material with semipinnate (or semidigitate) leaves from Svalbard combines characters of P. arenosa subsp. chamissonis and P. pulchella (rather than P. lyngei). In the parental model, this material should be assigned to this species (and nothosubspecies). Weassign it in this way. However, several of the observed populations indicate ongoing hybridization rather than a stabilized taxon (observed, e.g., in the Wijdefjord area in 2010 by Elven and Alsos).