Relationships of cucumbers and melons unraveled: molecular phylogenetics of Cucumis and related genera (Benincaseae, Cucurbitaceae).

Cucumis (Cucurbitaceae) comprises 33 species of annuals and perennials with a major native center of diversity in tropical and southern Africa. The genus includes some economically important and widely grown vegetables such as cucumbers and melons. Monophyly of the genus has been disputed in previous studies, but with only limited sampling. Relationships within Cucumis are thus poorly understood; moreover, the validity of the closely related genera has not been thoroughly tested. The present study was undertaken to test the monophyly of Cucumis and several closely related genera, to test sectional circumscriptions within Cucumis, and to understand the biogeographical history of the genus. We sequenced the nuclear ITS and plastid trnS-trnG regions for 40 ingroup and three outgroup taxa, representing all recognized subgenera and sections. Parsimony, maximum likelihood, and Bayesian analyses found Cucumella, Oreosyce, Mukia, Myrmecosicyos, and Dicaelospermum nested within Cucumis. The clades recovered within the Cucumis complex in some instances represent the first phylogenetically derived hypothesis of relationships, whereas others correspond to previous subgeneric and sectional classifications. At least four introductions from Africa to Asia, as well as one reintroduction to Africa, are suggested within the Cucumis complex. Cucumis sativus (cucumber) is strongly supported as sister to the eastern Asian C. hystrix, whereas C. melo (melon) is strongly supported as sister to C. sagittatus in southern Africa.