Panarctic Flora

641012 Potentilla aff. pensylvanica

Geography: American Beringian: ALA.

Notes: Elven and Murray: Species of sect. Niveae as circumscribed by Soják (1986, 1989, 2004) have ternate leaves, species of sect. Pensylvanicae have pinnate leaves. Soják and Yurtsev have consistently interpreted plants sharing other features with these sections, but with intermediate (semidigitate, semipinnate) leaves, to be hybrids between or hybrid species developed from crosses between species from the two sections. Soják (1986) treated and partly named numerous such hybrids and hybrid species and more have been added since. In the Arctic, at least 14 named hybrid species, one variety, and two unnamed hybrid species have been proposed with this intersectional parentage:

* Potentilla borealis from P. anachoretica x P. arenosa subsp. arenosa (Soják 1985b).

* Potentilla czegitunica from P. anachoretica x P. sect. Niveae (Yurtsev PAF proposal; Soják 2004).

* Potentilla dezhnevii from P. anachoretica x P. uniflora (Yurtsev PAF proposal) or perhaps from P. anachoretica x P. subvahliana (Ertter et al. 2011).

* Potentilla furcata from P. arenosa subsp. arenosa x P. bimundorum (Soják 1986) or from P. arenosa subsp. arenosa x P. litoralis (Ertter et al. 2011).

* Potentilla insularis from P. arenosa subsp. chamissonis x P. lyngei (Soják 1986).

* Potentilla murrayi from P. anachoretica x P. subvahliana (Yurtsev 1984b).

* Potentilla pedersenii from P. arenosa subsp. arenosa x P. pulchella (Soják 1986; Yurtsev PAF proposal).

* Potentilla petrovskyi from P. anachoretica x P. sp. sect. Niveae (Yurtsev PAF proposal) or from P. anachoretica x P. nivea (Soják 2004).

* Potentilla psychrophila from P. litoralis x P. nivea (Soják 2006).

* Potentilla rubricaulis ?[P. hookeriana Lehm.] from P. arenosa subsp. arenosa x P. bimundorum (Soják 1996; Ertter et al. 2011).

* Potentilla subquinata from P. nivea x P. pulchella (Soják 1986), but see notes to P. prostrata.

* Potentilla tolmatchevii from P. arenosa subsp. arenosa x P. pulchella (Yurtsev 1984b, PAF proposal).

* Potentilla tolmatchevii var. zubkovii from P. arenosa subsp. chamissonis x P. pulchella (Yurtsev 1984b, PAF proposal).

* Potentilla tschaunensis from P. anachoretica x P. nivea (Yurtsev 1984b, PAF proposal; Soják 2004).

* Potentilla uschakovii from P. pulchella x P. subvahliana (Yurtsev 1984b, PAF proposal).

* Potentilla sp. aff. uschakovii (Canadian Arctic Archipelago) from P. pulchella x P. subvahliana.

* Potentilla sp. aff. vahliana (Baffin Island) from P. pulchella x P. vahliana.

This may well be the most complicated and least resolved group of northern Potentillas. The PAF collaborators have not reached a consensus treatment. The discussions have concerned the assumed parentages but even more whether the proposed species are worthwhile or just swarms of not interconnected or well-spread local agamospermous biotypes ("populations") from many separate hybridizations. The group includes some species where we have documentation of significant, more or less consistent ranges and of at least some morphological uniformity, and many others where we do not have such information. These latter taxa are entered provisionally, in the majority of cases not because we have justified reasons to doubt them but because the abovementioned documentation is not available to all of us yet. We have not had the opportunity to survey the vast Russian collections or to translate the necessary literature.

Yurtsev (PAF proposal) accepted 11 species ranging from probably stabilized and comparatively wide-ranging ones to very local or very disjunct ones (assumed to have several origins) and Yurtsev (1984b, PAF proposal) and Soják (1986, 2004) suggested a specific parentage for each of them. From sect. Pensylvanicae, P. anachoretica is suggested to be parental in six cases, P. pulchella in three cases, P. litoralis in two cases, and P. bimundorum and P. lyngei in one case each. From sect. Niveae, taxa of the P. nivea aggregate and P. arenosa are suggested to be parental in eight cases, of the P. uniflora aggregate in 3-4 cases. As for relations with sect. Pensylvanicae, the Russian parts of the variation seem to have much affinity with P. anachoretica, the North American (perhaps except for Alaska) and the Greenland parts with P. pulchella, and the mainland North American parts also with P. bimundorum and P. litoralis (or P. pensylvanica s. lat.).

The identification of these hybrid species depends on specific combinations of characters assumed inherited from specific parents, sometimes resulting in very disjunct and obviously polytopic taxa. Firstly, in the European and North American interpretation, hybridity is not automatically assumed for such plants with semidigitate or semipinnate leaves. Their identification in that interpretation depends on the total character composition. Secondly, we would like to see some consistency (or at least explainability) in the geographical range as a criterion for separation between worthwhile species and scattered cases of hybridization and local agamic biotypes. We admit that also the North American, Greenland, and northern European taxa combine characters known from sect. Niveae and sect. Pensylvanicae but not that they therefore necessarily have originated from hybrids between extant species from these sections. In the single case that has been studied experimentally (P. insularis), the hypothesis of a hybrid origin is not well supported in molecular markers. The studies addressing this species rather say that the investigated material belongs to sect. Niveae, close to P. arenosa subsp. chamissonis, in which case occurrence of semidigitate and semipinnate leaves may be an inherent feature also of sect. Niveae.