Dilleniaceae are an angiosperm family consisting of 10-14 genera and; 500 described species, with a pantropical distribution extending into temperate Australia. This study addresses the infrafamilial relationships of Dilleniaceae with nucleotide sequence data from the plastid loci rbcL, infA, rps4, and the rpl16 intron. Analyses of these data using maximum parsimony and Bayesian methods resolve Tetracera, the only pantropical genus in the family, as sister to all other Dilleniaceae. Within the clade of Dilleniaceae exclusive of Tetracera, the New World endemic genera form a clade that is sister to a clade composed of the Old World endemic genera. The latter contains two major subclades: (1) a clade containing Acrotrema, Dillenia, and Schumacheria and (2) a clade containing Hibbertia and its satellite genera, Adrastaea and Pachynema, which are embedded within Hibbertia. Ancestral-state reconstructions of six morphological characters of both biological and taxonomic significance within Dilleniaceae suggest hypotheses of polarity or lability for each that differ substantially from those based on evolutionary trends. Perforation plate-type evolution within Dilleniaceae is equivocal, but the large majority of most parsimonious reconstructions suggest that simple perforation plates are plesiomorphic. Poorly organized leaf venation architecture is synapomorphic for Hibbertia s.l. Floral morphological features classically regarded as primitive, such as exceptionally large numbers of stamens (200+) and numerous carpels (more than isomerous with the corolla), are clearly derived within Dilleniaceae and are features of uncommon occurrence within the family as a whole. Both multicarpellate, synorganized gynoecia and monosymmetric androecia have multiple origins within the family. A new classification of Dilleniaceae is outlined, and nomenclatural changes necessitated by the phylogenetic results are provided.
