Historical biogeography of the herbaceous bamboo tribe Olyreae (Bambusoideae: Poaceae)

The tribe Olyreae comprises 124 understorey herbaceous bamboos species and almost all of its species are distributed in the Neotropics. Only Buergersiochloa bambusoides is found in New Guinea, and Olyra latifolia has a disjunct distribution in tropical America, Africa and Madagascar. Applying phylogenetic and biogeographical analyses, our aim was to identify the ancestral area and time of divergence of Olyreae, and to elucidate whether the bi-continental distribution of O. latifolia was the result of natural long-distance dispersal or human introduction. Our results confirmed the monophyly of tribe Olyreae, the paraphyly/polyphyly of the genus Olyra, and the sistership of Buergersiochloa bambusoides to the rest of Olyreae. Estimates of divergence time and ancestral range indicate that the Olyreae probably originated in the late Eocene to Oligocene, followed by Miocene diversification. South America+Oceania were recovered as the ancestral area of the tribe, therefore the distribution of B. bambusoides lies within the ancestral area. Our phylogenetic results showed that all O. latifolia samples, both American and African, formed a strongly supported clade. The lack of genetic differentiation indicates that probably the species was introduced to Africa very recently, potentially by humans during colonial times. Based on the widespread distribution of O. latifolia in Africa despite its lack of use by humans, we suggest that this species might possess effective capabilities for dispersal and establishment, both of which would require further study.