Panarctic Flora

500117-19 The Micranthes nivalis aggregate M. nivalis, M. rufopilosa, M. tenuis

Geography: Circumpolar-alpine.

Notes: Micranthes nivalis and M. tenuis are probably closely related. However, they differ constantly in morphology, ploidy levels, and partly in habitat choice. Transitional forms or hybrids have not been convincingly documented and must be very rare, if they exist, in spite of extensive sympatry. The ranges of the two species are nearly the same in the north but M. nivalis reaches much farther south than M. tenuis. They have for a long time been accepted as two species in Eurasia and Greenland but not until fairly recently in Canada (Healy and Gillespie 2004) and Alaska. The most evident difference is found in the multicellular scape hairs. These are long, entangled, and white in M. nivalis, short, more or less straight, and purplish or at least with purplish partition walls in M. tenuis. In addition, the leaf shape and teeth differ as do inflorescence structure (more or less open with a few, stalked flowers in M. tenuis, more compact with more numerous, often subsessile flowers in M. nivalis), petal shape, size, and colour, and fruit shape (beaks strongly recurved in M. tenuis, not in M. nivalis). Every well developed plant we have seen (Greenland, North America, Asia, Europe) can be assigned to species without any doubt.

A third species has been described and reported from the northern Cordilleran plants in Canada and Alaska: M. rufopilosa. It is similar to M. tenuis and M. nivalis in most of its features but differ from the former in presence of rusty hairs on the leaf lower surface, from both in a more open inflorescence and more rhombic leaves. Its ploidy level is not decided (but see below).