PHYLOGENETIC SYSTEMATICS AND BIOGEOGRAPHY OF THE GIGARTINACEAE (GIGARTINALES, RHODOPHYTA) BASED ON SEQUENCE-ANALYSIS OF RBCL

Recently Hommersand, Guiry, Fredericq and Leister (1993, Hydrobiologia 260/261 : 105-120) proposed a revised classification of the marine re d algal family Gigartinaceae in which sixty-nine species were classifi ed into four extant (Chondrus Stackhouse, Gigartina Stackhouse, Iridae a Bory, nom. cons., Rhodoglossum J. Agardh) and three reinstated (Chon dracanthus Kutzing, Sarcothalia Kutzing, Mazzaella G. de Toni f.) gene ra based on developmental and morphological criteria. We have undertak en a preliminary study of the phylogenetic systematics and biogeograph y of the Gigartinaceae based on an independent data set derived from s equence analysis of rbcL, the gene that codes for the large subunit of RuBisCO. The topology of the rbcL tree, which contains 43 species, ge nerally supports our recent systematic revision, while highlighting so me taxonomic problems. 'Gigartina' alveata occupies a basal position i solated from all other taxa. Chondracanthus forms a distinct clade wit h centers of speciation in East Asia and Pacific North America. The Gi gartina/Rhodoglossum clade is primarily austral and appears to have or iginated in the southwestern Pacific Ocean. Sarcothalia is antiboreal. Iridaea, 'Gigartina' skottsbergii, three Mazzaella clades, and Chondr us form a cluster partly localized in antiboreal waters but extending along Pacific South and North America to East Asia, with one species, Chondrus crispus, in the North Atlantic Ocean. We propose that ancestr al taxa belonging to the Gigartinaceae originated along the eastern ed ge of Gondwanaland in the Mesozoic and spread around the perimeter of the supercontinent Pangea giving rise to present-day genera in more or less linear sequence, followed by secondary dispersal of some species .