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 plastid-encoded rbcL sequences is presented for members of the Solieriaceae, an economically important family containing carrageenan-type phycocolloids. Previous studies established that the Solieriaceae sensu lato forms a terminal clade in the Solieriaceae complex, a cluster of families sister to the Gigartinaceae complex (Gigartinaceae and Phyllophoraceae). The family Solieriaceae (including the Areschougiaceae) presently contains about 20 genera that are widely distributed in warm-temperate and tropical waters throughout the world. Molecular rbcL and published morphological evidence are consistent 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 remaining genera , comprising the tropical and subtropical cluster, form a robust terminal clade (100% bootstrap support). This assemblage can be divided into seven groups, most of which receive strong bootstrap support: (1) Sarconema, (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' uncinatum from the Gulf of California. Four clusters of species are recognized in the Eucheuma group that correspond to the sections: Eucheuma, Gelatiformia (= Betaphycus), Anaxiferae, and Cottoniformia (= Kappaphycus) proposed by Maxwell Doty. No decision is reached regarding the taxonomic rank appropriate to the eucheumoid taxa.