Flora of North America species comparison

Subspecies 4 or 5 (4 in the flora).

Potentilla anserina is polymorphic in most features, especially in hairiness, but also in size and in degree of dissection of leaflets, epicalyx bractlets, and sepals. While most of the variation described by A. G. Blytt (1906) is taxonomically insignificant, A. Rousi (1965) found support for three northern races: subspp. anserina, egedei, and pacifica. He also suggested that P. yukonensis Hultén might qualify as a separate subspecies. This treatment follows J. Soják (1994) in accepting four northern subspecies of P. anserina, all present in North America.

A. Rousi (1965) demonstrated partial interfertility between the races of Potentilla anserina, which form intermediates in all zones of contact. The distinctness of the four races, in spite of intermediates, is upheld by being partly allopatric and occupying different habitats where they are sympatric. As partly interfertile parapatric entities, they are best treated as subspecies.

The vast majority of chromosome counts are tetraploid. Tetraploid plants (2n = 28) are fully fertile; hexaploids (2n = 42) are largely pollen and seed sterile; pentaploids (2n = 35) are probably occasional hybrids (S. Erlandsson 1942, 1942b; A. Rousi 1965). A. Kurtto et al. (in J. Jalas et al. 1972+, vol. 13) considered numbers above tetraploid level as cases of occasional autopolyploidy.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Although now restricted to plants with exclusively (or at least predominantly) cottony hairs on the petioles, the name Potentilla nivea has a long history with an often wider application, sometimes including nearly all of sect. Niveae. As further confusion, J. Soják (1989) noted that the Linnaean type of P. nivea belonged to what is here treated as P. arenosa. Although historical usage of P. nivea has been re-established as a conserved name with a conserved type (B. Eriksen et al. 1999), from 1989 to 1999 the name P. nivea was applied to P. arenosa. During this period, P. prostrata subsp. floccosa was briefly adopted as the correct name for this species (for example, W. J. Cody 1996).

Molecular evidence (B. Eriksen and M. H. Töpel 2006) indicates that populations of Potentilla nivea in the Atlantic regions, including Greenland and eastern Canada, differ from those in the Beringian regions of northwestern North America, suggesting expansion from separate Pleistocene refugia. A comparable pattern was noted by R. Elven and S. G. Aiken (2007) based on morphologic characters. The conserved type of P. nivea is from northern Sweden (Eriksen et al. 1999) and belongs to the Atlantic morphologic group. The variation within each region is large, and racial recognition would accordingly be premature. Plants from sites south of the continental glaciation, which were not included in the analysis by Eriksen and Töpel, deviate in having acuminate leaflet teeth and epicalyx bractlets and in being generally more slender. Epicalyx bractlets of some Washington plants are nearly as narrow as those of P. crebridens.

Additional chromosome numbers have been reported for Potentilla nivea, but it is unknown whether these apply to this species, P. crebridens, some Asian relative, or hybrids.

(Discussion copyrighted by Flora of North America; reprinted with permission.)