The taxonomic position of Hectorella caespitosa and Lyallia kergelensis, caespitose plants endemic to New Zealand and to the Kerguélen Archipelago of Antarctica, respectively, remains controversial. Some authors place them within Portulacaceae, but a slight majority of recent authorities treat them as a separate family, Hectorellaceae. Sequences of the chloroplast genes rbcL, ndhF, and matK were obtained from H. caespitosa and added to previously published sequences from Portulacaceae and related families. These data strongly supported the derived position of Hectorella within a clade consisting of western American members of Portulacaceae; the sister group of Hectorella was a clade including Montia, Claytonia, and Lewisia. Implications for taxonomy are discussed. In order to accomodate monophyly in tribal-level classification while preserving current tribes Montieae and Lewiseae, the new tribe Hectorelleae is proposed for the family Portulacaceae.