<p>Abstract</p> <p>Background</p> <p>The Cucurbitaceae genus <it>Trichosanthes</it> comprises 90–100 species that occur from India to Japan and southeast to Australia and Fiji. Most species have large white or pale yellow petals with conspicuously fringed margins, the fringes sometimes several cm long. Pollination is usually by hawkmoths. Previous molecular data for a small number of species suggested that a monophyletic <it>Trichosanthes</it> might include the Asian genera <it>Gymnopetalum</it> (four species, lacking long petal fringes) and <it>Hodgsonia</it> (two species with petals fringed). Here we test these groups’ relationships using a species sampling of c. 60% and 4759 nucleotides of nuclear and plastid DNA. To infer the time and direction of the geographic expansion of the <it>Trichosanthes</it> clade we employ molecular clock dating and statistical biogeographic reconstruction, and we also address the gain or loss of petal fringes.</p> <p>Results</p> <p><it>Trichosanthes</it> is monophyletic as long as it includes <it>Gymnopetalum</it>, which itself is polyphyletic. The closest relative of <it>Trichosanthes</it> appears to be the sponge gourds, <it>Luffa</it>, while <it>Hodgsonia</it> is more distantly related. Of six morphology-based sections in <it>Trichosanthes</it> with more than one species, three are supported by the molecular results; two new sections appear warranted. Molecular dating and biogeographic analyses suggest an Oligocene origin of <it>Trichosanthes</it> in Eurasia or East Asia, followed by diversification and spread throughout the Malesian biogeographic region and into the Australian continent.</p> <p>Conclusions</p> <p>Long-fringed corollas evolved independently in <it>Hodgsonia</it> and <it>Trichosanthes</it>, followed by two losses in the latter coincident with shifts to other pollinators but not with long-distance dispersal events. Together with the Caribbean <it>Linnaeosicyos</it>, the Madagascan <it>Ampelosicyos</it> and the tropical African <it>Telfairia</it>, these cucurbit lineages represent an ideal system for more detailed studies of the evolution and function of petal fringes in plant-pollinator mutualisms.</p
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