As a basis for inferring phylogenetic relationships between Pelvetia and Pelvetiopsis in the family Fucaceae, the complete sequences of the
plastid-encoded RuBisCo spacer region were determined for all four species of Pelvetia, for the type species of Pelvetiopsis, P. limitata, and
for three other fucacean species (Ascophyllum nodosum, Fucus gardneri and F. vesiculosus). All trees based on the sequences of the RuBisCo
spacer region showed that Pelvetia is not monophyletic and consists of two clades, one including P. babingtonii, P. compressa, and
P. siliquosa, the other comprising only the type species, P. canaliculata. P. canaliculata is not closely related to any of the other Fucaceae
studied, and it may represent a monotypic genus. RuBisCo spacer sequences support the establishment of a new genus for the three
Pacific Pelvetia species: P. babingtonii, P. compressa and P. siliquosa. The congruence of the RuBisCo spacer data with reported nuclear rDNA
18S and ITS sequences, and with biogeographical and morphological data, indicates that the RuBisCo spacer region, including its flanking
areas, is useful for inferring phylogenetic relationships within the Fucaceae.