The west coast endemic, Blepharostoma arachnoideum, is so infrequently encountered that its status as a species distinct from B. trichophyllum has been held in doubt. Despite its rarity, it displays a consistent set of vegetative characters, which may be used to separate it from all forms of B. trichophyllum. Blepharostoma trichophyllum subsp. brevirete, a form that intergrades with typical subsp. trichophyllum, has often been confused with B. arachnoideum. Blepharostoma arachnoideum is presently known from only 25 sites from northwestern California to southwestern British Columbia. Mature perianths have only recently been found in B. arachnoideum and are illustrated here and compared with perianths of B. trichophyllum.