A plastid DNA phylogeny ofDasymaschalon(Annonaceae) and allied genera: Evidence for generic non–monophyly and the parallel evolutionary loss of inner petals

Abstract

AbstractDasymaschalonand the closely related generaDesmos, FriesodielsiaandMonanthotaxistogether comprise ca. 170 species of trees, shrubs and woody climbers distributed in tropical Africa and tropical Asia. These genera form the desmoid clade, which, because of the presence of diverse flower and fruit syndromes including different types of pollination chambers and moniliform monocarps, offers an opportunity to investigate potentially ecologically significant shifts in flower and fruit characters. Despite its morphological diversity, however, generic delimitation within the desmoid clade is problematic and the intergeneric relationships of the constituent genera are only poorly understood. Bayesian, maximum likelihood and maximum parsimony analyses of plastid DNA sequence data (matK, psbA–trnH, ndhF, rbcL, trnL–F; ca. 5.4 kb; 52 taxa) were used to clarify phylogenetic relationships within the desmoid clade. The evolution and taxonomic utility of selected fruit and flower characters was investigated with likelihood and parsimony ancestral character reconstructions. The results indicate problems in the current delimitations ofDasymaschalonandFriesodielsia. Friesodielsiaas currently circumscribed is polyphyletic, with AfricanFriesodielsiaspecies allied to the African genusMonanthotaxis, and only distantly related to Asian representatives. The majority ofDasymaschalonspecies form a strongly supported clade, but three species are more closely related to Asian species ofFriesodielsia. Ancestral character reconstructions indicate that seed number and monocarp shape are of limited value in generic circumscriptions, and that the three–petalled corolla characteristic ofDasymaschalonevolved independently twice within the desmoid clade. Disruptions to homeotic gene expression or strong selective pressure for a partial enclosure of the mature stamens and carpels by the corolla are hypothesised to underlie the parallel evolution of pollination chambers formed by outer petal homologues subsequent to inner petal loss.