A cladistic analysis of species groups in Weinmannia (Cunoniaceae) based on morphology and inflorescence architecture

Weinmannia (Cunoniaceae) is a woody genus of about 150 species widely distributed in the tropics and the southern temperate zone. Herbarium and living specimens were examined to determine characters for a cladistic analysis to test the monophyly of the genus and its sections. A matrix of 28 taxa and 31 morphological characters was analyzed to find the most parsimonious trees. The strict consensus cladogram supports the monophyly of the genus Weinmannia and sections Leiospermum, Weinmannia (including sect. Simplicifolia), Inspersa, and Spicata, but section Fasciculata is paraphyletic with respect to a highly derived section Weinmannia. Section Leiospermum from the South Pacific is the sister taxon to the rest of the genus. Some of the most parsimonious trees support a monophyletic clade from Madagascar of sections Inspersa and Spicata, but this node is unresolved in the strict consensus tree. Although the deep nodes of the phylogeny are not well supported, and few evolutionary interpretations are ventured, it appears that dioecy has arisen independently at least three times in the genus. The method and theory used to analyze variation in inflorescence architecture, which emerges from the metameric construction of plants and positional homology, are emphasized. The cladistic coding of positional characters and the tracing of their evolution on the cladogram are a study in heterotopy, i.e., evolutionary change in the position of development. Heterotopic evolution in the inflorescence is common in Weinmannia, suggesting a role for an evolutionary-developmental process that has typically been overlooked in favor of heterochrony.