Largely due to the use of relative differences, the separation of species in the Grimmia longirostris-G. pilifera complex has often proven problematic. Using character combinations of stem anatomy, seta/capsule lengths, and sexuality we recognize four species in the complex in North America and demonstrate that G. arizonae and G. catalinensis, both lost in synonymy, are good species. Grimmia pilifera typically has long, acuminate apices with a short ovate base, short awns, and lacks a central strand (Cao and Vitt 1986, Crum 1994, Greven 1999). Grimmia arizonae has broader, ovate-lanceolate leaves, long awns, and a central strand. However, Munoz (1999) synonymizes G. arizonae with G. pilifera, dismissing their differences as a result of locality variation and sexual development. He reports that in eastern North America, and in shade, G. pilifera has its typical form. However, in the west, and in sun, leaves are ovate-lanceolate without distinct bases. To him, the absence of a central strand, is “too variable to be reliable;” fertile stems have a distinct strand, sterile stems have none. By contrast, we found no correlation between sexual maturity and strand development; sterile or fertile G. pilifera lack a central strand. Further, its stem epidermis is consistently 2x thicker than G. arizonae. In the west there are specimens without a central strand, long, acuminate apices and ovate bases (G. pilifera) and others with a central strand, and broadly ovate-lanceolate leaves (G. arizonae). Both Munoz and Greven classify G. catalinensis as G. longirostris with immersed capsules. However, specimens with long setae (G. longirostris) are cladautoicous, while specimens with short setae (G. catalinensis) are gonioautoicous. Thus we recognize four species. Grimmia longirostris: cladautoicous, exserted capsules, with a central strand. Grimmia catalinensis: gonioautoicous, immersed capsules, with a central strand. Grimmia arizonae: dioicous, immersed capsules, with a central strand. Finally, G. pilifera: dioicous, immersed capsules, and no central strand.

Key words: central strand, Grimmia, Grimmiaceae, taxonomy