Systematics and character evolution in Durio s. lat. (Malvaceae/Helicteroideae/Durioneae or Bombacaceae-Durioneae)

A molecular phylogenetic study of Durio s.lat. was conducted based on sequences of the internal transcribed spacer (ITS) of nuclear ribosomal DNA for 30 ingroup exemplars, representing 16 species, and two taxa of Cullenia as outgroups. The phylogeny suggests the existence of two well-circumscribed clades composed, respectively, of species with poricidal pollen locules ( Boschia) and species with pollen locules that open with longitudinal slits ( Durio s.str.). The latter clade is subdivided into two strongly supported clades: /Tubulidurio, with highly fused filaments and free calyx lobes, and /Palatadurio, with largely free filaments and connate calyx lobes. We provide phylogenetic definitions for the names of these well-supported clades. Reconstruction of floral evolution is consistent with the hypothesis that vertebrate pollination is ancestral for Durio s.lat. and Cullenia. However, there have been further shifts in pollination system within Durio s.lat., which may account for some of the current diversity of floral characters. The correlation of fruit and aril characteristics suggests that there are two major dispersal syndromes, involving either birds (fruits opening on trees; aril red/yellow and odorless) or terrestrial mammals (fruits opening only after falling to the ground; aril pale colored and pungent). The distribution of extant taxa implies a Malesian origin and radiation of the study group, with a single dispersal of Cullenia to India and Sri Lanka. However, the fossil pollen record raises the possibility that Durio and relatives may have migrated to Southeast Asia from the Indian subcontinent after it collided with Asia. A molecular clock analysis suggests that the earliest divergence within the study group occurred about 20 to 32 mya and, hence, does not favor either biogeographic scenario.