Four populations of the newly described freshwater red algal species Batrachospermum spermatoinvolucrum were sampled from British Columbia on the west coast of North America and Labrador on the east. The rDNA internal transcribed spacer (ITS) 1 and 2 sequences, RUBISCO large subunit (rbcL) gene data for three of the populations and morphometric characteristics were compared with those of B. gelatinosum. In addition, the key feature distinguishing B. spermatoinvolucrum, spermatangia on the involucral filaments of the carpogonial branch, was investigated seasonally in one British Columbia population of this species. The ITS analysis suggested that the B. spermatoinvolucrum populations were more closely related to particular B. gelatinosum populations than to each other and did not form a monophyletic clade. Two populations of B. spermatoinvolucrum from Labrador and British Columbia had identical rbcL sequences that were distinct from that of B. gelatinosum. However, the rbcL sequence from the third population of B. spermatoinvolucrum differed by only one nucleotide substitution from the B. gelatinosum populations. The tree generated from the morphometric data showed two groupings, each containing populations of both taxa. The presence of spermatangia-bearing involucral filaments was a stable character throughout the year. On the basis of these findings, B. spermatoinvolucrum is reduced to a form of B. gelatinosum. This form would encompass variant populations with characteristic carpogonial involucral filaments bearing spermatangia.