A giant spurrey on a tiny island: on the phylogenetic position of Sanctambrosia manicata (Caryophyllaceae) and the generic circumscriptions of Spergula, Spergularia and Rhodalsine

The only member of the generally herbaceous family Caryophyllaceae that may grow to a small tree is Sanctambrosia manicata, endemic to remote San Ambrosio Island, off the coast of Chile. The monospecific Sanctambrosia has been suggested to be closely related to Spergula and Spergularia (spurreys) on the basis of morphology, despite its treelike habit and gynodioecy. A plastid DNA dataset (ndhF, rps16, trnL-F) is used to investigate the relationships of Sanctambrosia and other members of Sperguleae. Sanctambrosia manicata is shown to be nested in a clade of New World and Australian Spergularia and the new combination Spergularia manicata is proposed. The volcanic San Ambrosio has been estimated to be almost three million years old, and S. manicata presumably evolved its treelike habit and gynodioecy over a short period of time. Spergula and Spergularia are monophyletic and recognizable by their number of carpels, five in Spergula and three in Spergularia. Spergularia fallax, which resemb...