Caulerpa (Chlorophyta, Ulvophyceae) is a common marine
tropical-subtropical genus of about 70 species, inhabiting the eulittoral
rocks and corals as well as mangroves. The genus is particularly diverse
and abundant along southern Australian coasts, where it is
thought to have originated. Here, we compare sequences from the nuclear
ribosomal cistron among five species of Caulerpa, including
nine populations of Caulerpa filiformis from two biogeographic
five from Australia and four from South Africa. Species
relationships were well resolved by internal transcribed spacer (ITS)
sequences and supported by high bootstrap values as follows: (C.
geminata (C. simpliciuscula (C. trifaria (C.
scalpelliformis (C. filiformis – Australia, C.
– South Africa))))). Nucleotide divergence
within C. filiformis was low with four and five nucleotide
differences present in ITS1 and ITS2 respectively. Unexpectedly, the 5.8S
gene showed eight nucleotide differences between the Australian and South
African populations and may indicate cryptic species. The
Australian C. filiformis is probably not a South African
introduction. These sequences provide an independent means for assessment
species relationships and appear, in so far as limited taxon sampling permits,
to follow chloroplast ultrastructural groupings proposed 20 years ago.