Flora of North America species comparison

The bright, silvery vestiture of the leaves quickly distinguishes Potentilla argentea from P. inclinata and P. intermedia. Although treated here as introduced, some (P. A. Rydberg 1898; P. A. Werner and J. D. Soule 1976) considered P. argentea to be probably native in eastern North America.

The Potentilla argentea species group is an amphi- or apomictic polyploid complex that has been the subject of numerous cytological, sexual, and molecular studies (for example, A. Müntzing and G. Müntzing 1945; A. Müntzing 1958; J. Paule et al. 2011). Taxonomic treatments have ranged from a highly polymorphic single species to an abundance of species, varieties, and forms (T. Wolf 1908). This treatment is at the conservative end of the spectrum. Some New England references (R. C. Bean et al. 1967; F. C. Seymour 1969) distinguish plants with densely white-hairy adaxial leaflet surfaces as var. pseudocalabra Th. Wolf, a name based on plants from southeastern Europe. Molecular analysis by Paule et al. supports the conclusion by Wolf that the variety consists of intermediates between P. argentea and P. calabra Tenore. The optimum taxonomic disposition of var. pseudocalabra, and whether any North American plants are properly included, remains to be determined.

Potentilla argentea has been reported as an active agent in treating cirrhosis of the liver (N. T. Starostenko and V. N. Starostenko 1971).

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

Potentilla norvegica is considered native in both North America and Eurasia, with the American race occasionally recognized as subsp. hirsuta for the stiff hairs on the stems, petioles, and pedicels of most plants in the flora area. This feature and other purported differences between the two races, in addition to being relatively subtle and inconstant, can be found in both America and Eurasia, though undoubtedly at least in part as introductions. Some populations in eastern Canada with glabrous stems have been distinguished as var. labradorica (for example, M. L. Fernald 1950), but such plants typically are intermixed with hairy individuals. The Löves (Á Löve 1954; Á Löve and D. Löve 1966) have argued that all three variants should be treated as distinct species due to chromosomal differences (hirsuta 2n = 56; labradorica 2n = 42; norvegica in the narrow sense 2n = 70) and obligate apomixis. Further research is needed to determine the taxonomic validity and rank of these expressions. If treated as species, P. flexuosa antedates P. labradorica (as noted by J. Soják 1969), while P. monspeliensis, although commonly used for the American race, is based on a European type (as summarized by A. Kurtto et al. in J. Jalas et al. 1972+, vol. 13).

An even greater challenge is determining native versus introduced ranges, especially given the likelihood that both native and Eurasian populations are widespread in North America. Achenes are produced prolifically and easily dispersed, to the extent that Potentilla norvegica is a contaminant in clover and hay fields and considered a weed at least in Canada (P. A. Werner and J. D. Soule 1976).

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