Polemonium villosum (Polemoniaceae) infraspecific taxa of northwest North America

Polemonium villosum Rud. ex Georgi (tall Jacob's-ladder) is a morphologically diverse species with a geographical range that extends from northern Idaho (USA) to the Arctic Ocean in northwest North America (47–71°N). A multivariate analysis of quantified morphological variables in conjunction with qualitative characteristics suggests the occurrence of two subspecies ( villosum and arctoalpinum), three varieties, and six taxonomic forma in the plant population. The varieties include the autonym villosum, which morphologically approximates the species’ isotype, and macrophytum W.L Strong and arctoalpinum W.L Strong (var. nov.). The varieties are distinguishable based on where leaves occur along the stem and the length of the longest mid-stem leaf. The varieties villosum and macrophytum have cauline leaves, but macrophytum lacks an assemblage of lower stem leaves and is a more robust plant (40–90 cm tall) with larger cauline leaves than villosum. The varieties villosum and arctoalpinum can be similar with respect to lower stem leaves and stature (typically <40 cm), except arctoalpinum has cauline leaves <15 mm long. The two subspecies have allopatric distributions, with arctoalpinum confined to high-latitude arctic and lower-latitude alpine sites. Reports of neither var. arctoalpinum nor var. villosum in the southwest half of Alaska may be for ecological or specimen collection reasons.