Morphology, ploidy and molecular phylogenetics reveal a new diploid species from Africa in the baobab genus Adansonia (Malvaceae: Bombacoideae)

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The genus Adansonia has a disjunct geographical distribution: six species are endemic in Madagascar, one in Africa, and one in Australia. The well-known African baobab (Adansonia digitata) is an iconic tree with considerable ethnobotanical significance. In contrast to the other seven species, which are diploid, A. digitata is tetraploid. A common ancestor of A. digitata and the other diploid baobab species would be diploid; however, there are no diploid species recorded on the African mainland. Examining variation in floral and pollen characters and chromosome number in specimens from Africa identified a new diploid baobab species, Adansonia kilima sp. nov., which co-exists with A. digitata in Africa. Adansonia kilima is restricted to moderate elevations (650–1500 m), in contrast to A. digitata, which is widespread throughout Africa but prefers elevations below 800 m. Adansonia kilima is superficially similar to A. digitata, but can be differentiated on the basis of floral morphology, pollen, and chromosome number. We used two chloroplast DNA markers and the nuclear ITS to examine phylogenetic relationships within Adansonia. Three lineages were observed: one containing the Malagasy species, one containing the Australian species, and one containing the African species. The relationships between these clades were difficult to resolve, but a link between the African and Australian clades emerged when the analysis used fewer replicate samples of individual Malagasy taxa, included indel characters and included fewer outgroup taxa. The ITS phylogeny demonstrated that A. digitata and A. kilima are genetically similar, suggesting that tetraploidy evolved relatively recently.


Document Type: Research Article

Affiliations: 1: Queensland Brain Institute, The University of Queensland, St Lucia 4072, Australia, Australian Institute for Bioengineering and Nanotechnology, The University of Queensland, St Lucia 4072 Australia;, Email: 2: Royal Botanic Gardens Melbourne, Birdwood Avenue, South Yarra, Victoria 3141, Australia, School of Geography and Environmental Sciences, Monash University, Clayton, Victoria 3800, Australia 3: School of Anatomical Sciences, Faculty of Health Science, University of the Witwatersrand, Johannesburg, Gauteng, 2193, South Africa 4: Centre for Microscopy & Microanalysis, The University of Queensland, St Lucia 4072 Australia 5: Pretoria National Herbarium, Cussonia Ave, Bremmeria 0001, South Africa 6: East African Herbarium, Museum Hill Road, P. O Box 45166, 00100 Nairobi, Kenya 7: Australian Institute for Bioengineering and Nanotechnology, The University of Queensland, St Lucia 4072 Australia

Publication date: December 14, 2012

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