The taxonomy of Arnica frigida and A. louiseana (Asteraceae)

Abstract

The systematic relationships of the Arnica frigida–louiseana complex have been evaluated. This complex has been previously recognized as one species. A. louiseana, with three infraspecific taxa: subspecies frigida, griscomii, and louiseana. Morphological, phytogeographical, and cytological data support the recognition of A. frigida ssp. frigida and the newly proposed combination A. frigida spp. griscomii. Arnica louiseana is also recognized at the specific level. All three taxa have distinct geographic distributions: A. frigida spp. frigida is found from eastern USSR, Alaska, Yukon, east to the Mackenzie River, N.W.T., with isolated populations east of the Mackenzie River and in northern British Columbia; A. frigida ssp. griscomii is extremely localized in Gaspé, Qué., and in northwest Newfoundland; and A. louiseana is restricted to high elevations in the Rocky Mountains of Alberta. The basic chromosome number for this complex is x = 19, with A. frigida ssp. frigida 2n = 38, 57, 76, and 95, A. frigida ssp. griscomii 2n = 76, and A. louiseana with chromosome complements of 2n = 76 and 95. This complex is predominantly apomictic with amphimictic phases in unglaciated Alaska. Disjunct distributions are probably the result of Pleistocene survival in refugia with apomictic phases being responsible for the recolonization of glaciated areas.