Observations on the phylogenetic systematics and biogeography of the Solieriaceae (Gigartinales, Rhodophyta) inferred from rbcL sequences and morphological evidence

A hypothesis of phylogenetic relationships inferred from analysis of plasti d-encoded rbcL sequences is presented for members of the Solieriaceae, an e conomically important family containing carrageenan-type phycocolloids. Pre vious studies established that the Solieriaceae sensu lato forms a terminal clade in the Solieriaceae complex, a cluster of families sister to the Gig artinaceae complex (Gigartinaceae and Phyllophoraceae). The family Solieria ceae (including the Areschougiaceae) presently contains about 20 genera tha t are widely distributed in warm-temperate and tropical waters throughout t he world. Molecular rbcL and published morphological evidence are consisten t with an Australasian origin for the family and a Tethyan distribution for its tropical representatives from west to east as far as the Pacific coast of North and South America. The austral lineages (Callophycus, Rhabdonia, Areschougia and Erythroclonium) are resolved at the base of the tree. The r emaining genera , comprising the tropical and subtropical cluster, form a r obust terminal clade (100% bootstrap support). This assemblage can be divid ed into seven groups, most of which receive strong bootstrap support: (1) S arconema, (2) a Eucheuma group, (3) an Atlantic Solieria group, (4) an Indo -Pacific Solieria robusta group, (5) a Meristiella/Meristotheca group, (6) Agardhiella and (7) a Sarcodiotheca group that includes 'Eucheuma' uncinatu m from the Gulf of California. Four clusters of species are recognized in t he Eucheuma group that correspond to the sections: Eucheuma, Gelatiformia ( = Betaphycus), Anaxiferae, and Cottoniformia (= Kappaphycus) proposed by Ma xwell Doty. No decision is reached regarding the taxonomic rank appropriate to the eucheumoid taxa.