Analysis of plastid rbcL DNA sequence data of the pantropical family Phyllanthaceae (Malpighiales) and related biovulate lineages of Euphorbiaceae sensu lato is presented. Sampling for this study includes representatives of all 10 tribes and 51 of the 60 genera attributed to Euphorbiaceae-Phyllanthoideae. Centroplacus and Putranjivaceae (Phyllanthoideae-Drypeteae) containing a paraphyletic Drypetes are excluded from Phyllanthaceae. Croizatia, previously thought to be a "basal" member of Euphorbiaceae-Oldfieldioideae (Picrodendraceae), falls within Phyllanthaceae. Phyllanthaceae with the mentioned adjustments form a monophyletic group consisting of two sister clades that mostly correspond to the distribution of tanniniferous leaf epidermal cells and inflorescence structure. With the exception of bigeneric Hymenocardieae and monotypic Bischofieae, none of the current Phyllanthoideae (Phyllanthaceae) tribal circumscriptions are supported by rbcL. Antidesma, Bischofia, Hymenocardia, Martretia, and Uapaca, all of which have previously been placed in monogeneric families, are confirmed as members of Phyllanthaceae. Savia is polyphyletic, and Cleistanthus appears paraphyletic. Paraphyly of Phyllanthus is also indicated, but this pattern lacks bootstrap support. Morphological characters are discussed and mapped for inflorescence structure, tanniniferous epidermal cells, breeding system, and fruit and embryo type. A table summarizes the main characters of six euphorbiaceous lineages.