538 Cypripedium calceolus L.

This calciphilous, mainly boreal species is reported among the amphi-atlantic plants (Hultén, Amphiatl., p. 280 and map 261) but has a tendency towards a circumpolar distribution. In N. America three slightly confluent varieties are distinguished, viz. var. parviflorum (Salisb.) Fem., var. pubescens (W illd.) Corell and var. planipetalum (Fem.) Vict. & Rouss. (cf. Femald, Manual 1950, p. 467). Cf. also Meusel et al. 1965, map p. 104.