The bryophyte flora of the Pacific Northwest includes three previously known species of tuber-producing hornworts that occupy seasonally dry habitats. Except for Phymatoceros bulbiculosus (Brot.) Stotler, W.T. Doyle & Crand.-Stotl., which was recently segregated from Phaeoceros Prosk. on the basis of a combination of morphological and molecular studies, no comprehensive studies of these taxa have been undertaken since their naming. As a consequence, confusion exists regarding their taxonomic identity. This study combines field observations with morphological and molecular data to evaluate the systematic status of Phaeoceros hallii (Austin) Prosk. and Phaeoceros pearsonii (M. Howe) Prosk. These data support the recognition of a new species, Phaeoceros proskaueri Stotler, Crand.-Stotl. & W. T. Doyle, in this complex of related taxa. In addition, morphological studies of the lectotype of Anthoceros tuberosus Taylor (= Phaeoceros tuberosus (Taylor) Prosk.), which is formally designated here, and the holotype of Paraphymatoceros diadematus Hässel demonstrate that neither is related to P. hallii, P. pearsonii or P. proskaueri. Phaeoceros tuberosus is aligned with P. laevis (L.) Prosk. and Paraphymatoceros hallii (Austin) Hässel is placed as a synonym of Phaeoceros hallii. Paraphymatoceros diadematus is postulated to be congeneric with Phaeomegaceros Duff et al., and the following new combinations are made: Paraphymatoceros fimbriatus (Gottsche) Stotler, Paraphymatoceros coriaceus (Steph.) Stotler, Paraphymatoceros hirticalyx (Steph.) Stotler, and Paraphymatoceros skottsbergii (Steph.) Stotler.