Phylogenetic relationships of the durians (Bombacaceae-Durioneae or /Malvaceae/Helicteroideae/Durioneae) based on chloroplast and nuclear ribosomal DNA sequences

The circumscription and phylogenetic position of the tribe Durioneae (Bombacaceae or /Malvaceae/Helicteroideae) was investigated by supplementing a previously published ndhF data set. The present analysis supports a narrow conception of Durioneae (excluding Camptostemon and Papuodendron) and confirms a close relationship with Helicteres, Reevesia, Ungeria, and Triplochiton (all of traditional Sterculiaceae). Phylogenetic relationships within Durioneae were inferred from a combined analysis of ndhF and ITS sequences. These data suggest that Neesia is sister to a clade comprising all other five genera of core Durioneae, and that Coelostegia + Kostermansia form a clade that is sister to Cullenia + Boschia + Durio. Various morphological features support these relationships. However, characters usually considered diagnostic for the entirety of Durioneae, such as a densely lepidote lower leaf surface and uni- or polylocular anthers, appear to be apomorphic within this clade. Likewise, spiny fruits and large arils covering the seeds are not plesiomorphic for Durioneae, in contradiction to Corner's classic Durian Theory. The phylogeny suggests that bat- and bird-pollination evolved from beetle-pollination and that this transition was coincident with extensive androecial modification. Similarities due to convergent evolution of floral traits in relation to pollination by birds and mammals probably account for the erroneous, traditional placement of Durioneae in Bombacaceae.