Floral development in Asteropyrum (Ranunculaceae): implications for its systematic position

Systematic affinities and taxonomical rank of Asteropyrum in the Ranunculaceae have been controversial. It has been placed in Coptidoideae, Thalictroideae, Ranunculoideae (incl. Helleboroideae),or sometimes in its own tribe or subtribe. Recent molecular phylogenetic studies, however, supported the inclusion of Asteropyrum in its own tribe Asteropyreae (Ranunuculoideae) but its affinities remain unclear. In order to help resolve such an uncertainty, we used scanning electron microscopy to study the floral development of A. peltatum ssp. cavaleriei. Our results indicated that the petal, carpel and ovule development in Asteropyrum markedly differs from that in Coptis (Coptidoideae) and Dichocarpum (Thalictroideae), whereas the inclusion of Asteropyrum in Ranunculoideae is supported by several floral morphological and developmental characters. Together with vegetative, anatomical, and cytological data from earlier comparative studies, our study indicates that the monotypic tribe Asteropyreae should be maintained.