Physoderma calami, a chytrid (Phycomycetes), has not been studied or apparently even collected in Europe since 1895 and has never been recorded in this hemisphere. Material widely distributed in herbaria indicated it was a Physoderma but no details save color, shape, and size or resting spores were known. A study of living material from Vermont indicates resting spore germination occurs by dehiscence of a lid and production of a sporangium with zoospores. The latter may form either an epibiotic or "ephermeral" sporangial stage and zoospores, or an endobiotic one, with extensive polycentric thallus bearing turbinate cells along the rhizoids, and, as outgrowths of these turbinate cells, straw-colored, thick-walled resting spores. The latter stage produces dark-brown spots on infected parts of the host.