Flora of North America species comparison

Potentilla subjuga is centered in the high mountains of Colorado and barely enters New Mexico in the Sangre de Cristo Mountains. Collections from Alberta also apparently belong to this species, but all known collections from Wyoming have been identified as different taxa, at least one currently undescribed. At its most distinctive, P. subjuga is easily recognized by its unique leaf division, with five palmate leaflets subtended by an additional pair (or two) of lateral leaflets. Southern populations, however, are more likely to have only three apical leaflets. The leaflets tend to be strongly bicolored with overlapping teeth, in contrast to most sympatric pinnate species. Petiole vestiture is also distinctive in being seasonally dimorphic, with long hairs on first-formed leaves spreading to ascending and those on later formed leaves tightly appressed, as well as more conspicuously verrucose. Unresolved infraspecific variation exists, and field observations suggest that P. subjuga readily hybridizes with sympatric species, creating a swarm of intermediate specimens.

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

Potentilla villosula was included previously in P. villosa; the two overlap in the southern and western Alaskan coasts, where a transition is suspected to be associated with differing ploidy levels. The plants from this area with silky hairs and multiflowered inflorescences are assigned to P. villosa; P. villosula has thicker, stiffer, and less silky hairs, fewer teeth per leaflet, narrower bracts, fewer and smaller flowers with narrower epicalyx bractlets and sepals, and fewer achenes (sometimes with single apical hairs). While P. villosa is restricted to relatively rocky sites near the coast from western Alaska to Oregon, P. villosula often occurs on coastal sand dunes, farther inland, and/or farther to the north.

As circumscribed, Potentilla villosula is a major plant of Alaska, especially of the Bering Sea region. The species extends from Alaska and the Yukon to at least central British Columbia. Most of the range given by E. Hultén (1968) for P. villosa belongs to P. villosula. W. J. Cody (1996) accepted the name P. villosula for a common south-central Yukon plant, but the majority of the plants mapped by Cody probably belong to P. subgorodkovii (although the distinction between the two species needs more resolution). Provisionally included here are plants from southern and central Yukon south through the Canadian Rockies, possibly including the type of P. nivea subsp. fallax A. E. Porsild. Such plants tend to be significantly smaller overall than Alaskan P. villosula; at least some have straight hairs on carpel apices.

J. Soják (2004) believed that Potentilla villosula evolved from crosses between P. villosa and P. vulcanicola. The affinity with P. villosa is seen in the sericeous vestiture, number of leaflet teeth, and flower number and size, and with P. vulcanicola in the frequent occurrence of straight hairs on carpel apices in both species. Plants with columnar caudex branches, representing a significant part of the Alaskan material, have been called subsp. congesta. This morphology results from the persistence of marcescent whole leaves for several years (in typical P. villosula only sheaths and petioles are retained). This character suggests that P. subvahliana, with which the form called subsp. congesta is sympatric, may be part of its parentage. Potentilla villosula is accepted here in a fairly collective sense, possibly including several hybrid lineages, but with P. villosa a part of them all.

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