Rosy pussytoes (Antennaria rosea), a common montane wildflower through much of western North America, is only rarely encountered in the Boise Front, at the edge of its range in the Conifer Zone. Only two small native populations are currently known within the floristic area, near Aldape Summit and Bogus Basin, though more are probably present at other sites along the Boise Ridge.
The choice of scientific name (Antennaria rosea or A. microphylla) for the majority of rosy pussytoes populations depends in large part on whether the source floristic reference is emphasizing precision or practicality. This is because rosy pussytoes is a member of a fascinating and well-studied evolutionary scenario known as a polyploid agamic complex or polyploid pillar complex. Instead of following the classic evolutionary pattern of repeated bifurcation from a common ancestor, a number of diploid ancestors repeatedly hybridize, with the progeny continuing to propagate in complex polyploid networks.
Within this framework, Antennaria microphylla is the primary diploid progenitor of the Antennaria rosea polyploid complex. The key morphological feature for recognizing diploids in Antennaria is that they are dioecious, meaning some plants have only staminate (male) flowers, while others have only pistillate (female) flowers, allowing normal sexual reproduction. In contrast, agamic polyploids usually bypass sexual reproduction, setting seed without requiring pollination; as a result, only plants with pistillate flowers occur in a population of Antennaria rosea in the narrow sense. In addition, A. microphylla in the narrow sense usually has stipitate-glandular hairs on the upper stem and white phyllaries. In contrast, A. rosea purportedly lacks stipitate-glandular hairs, and the phyllaries are more often red or pink than white. In practice, however, these distinctions are not always easily discernible, leading to some of the more pragmatically focused treatments (e.g., Cronquist 1994 in Intermountain Flora; Legler et al. 2018 in Flora of the Pacific Northwest) to include A. rosea within an expanded A. microphylla (the name with priority). According to Legler et al., “Pl[ant]s with bright pink phyllaries in the A. rosea complex sometimes have glandular st[em]s, and are inconsistently separable from A. microphylla.”
If precision is preferred over accuracy, one is furthermore faced with a choice of several subspecies within Antennaria rosea, distinguished by leaf length, phyllary color, number of heads, and flower size. All four subspecies recognized by Bayer (2006, Flora of North America) occur in Idaho. Collections from the Boise Front seem to be closest to A. rosea ssp. rosea, but this identification is far from unequivocal.
By whatever name, this charming plant is a delight to find in the wild, and a relatively forgiving addition to the garden.
Bayer, R. J. 1990. Investigations into the evolutionary history of the Antennaria rosea (Asteraceae: Inuleae) polyploid complex. Pl. Syst. Evol. 169: 97–110.