The names of two eastern North Pacific kelps (Phaeophyceae, Laminariales, Alariaceae) were inadvertently validated by Josephine Tilden on labels to specimens distributed in the exsiccata “American Algae”. Lectotypes for Lessonia littoralis and Pleurophycus gardneri, which concomitantly are the types of the names of the monospecific genera Lessoniopsis and Pleurophycus, respectively, are herein designated from among specimens housed in the Herbarium of the University of Minnesota, Tilden's home institution. Lessoniopsis ranges from Kodiak Island, Alaska, to the Big Sur coast of Monterey County, California, whereas Pleurophycus ranges from southeastern Alaska to Pt. Piedras Blancas, San Luis Obispo County, California. Molecular data suggest that both Lessoniopsis and Pleurophycus belong to the Alariaceae, a departure from their previous familial placements in the Lessoniaceae and Laminariaceae, respectively.