Study of the north Alaskan brown algal epiphyte Chukchia pedicellata sp. nov. suggests an apparently close relationship to Phaeostroma. Phaeostroma endophyticum S. Lund from east Greenland, Bylot Island, Nunavut, Canada, shows generic identity with Chukchia and specific differences from C. pedicellata. Comparison of C. pedicellata and P. pustulosum Kuck. (the type species of Phaeostroma) shows morphological, cytological, reproductive, and distributional differences. We recognize novelty of C. pedicellata and necessity to broaden the species description of P. endophyticum, which becomes Chukchia endophytica. C. endophytica is distinguished by its dimorphic vegetative habit, its large plurilocular sporangia, and the putative ability of the sporangia to digest host tissue to accommodate development within the host. Absence of pyrenoids and novel plurilocular sporangia in both species suggests that they are not members of the Ectocarpales, sensu lato.