Diversification into novel habitats in the Africa clade of Dioscorea (Dioscoreaceae): erect habit and elephant's foot tubers.
Dioscorea is a widely distributed and highly diversified genus in tropical regions where it is represented by ten main clades, one of which diversified exclusively in Africa. In southern Africa it is characterised by a distinct group of species with a pachycaul or "elephant's foot" structure that is partially to fully exposed above the substrate. In contrast to African representatives of the genus from other clades, occurring mainly in forest or woodland, the pachycaul taxa and their southern African relatives occur in diverse habitats ranging from woodland to open vegetation. Here we investigate patterns of diversification in the African clade, time of transition from forest to more open habitat, and morphological traits associated with each habitat and evaluate if such transitions have led to modification of reproductive organs and mode of dispersal.



The Africa clade originated in the Oligocene and comprises four subclades. The Dioscorea buchananii subclade (southeastern tropical Africa and South Africa) is sister to the East African subclade, which is respectively sister to the recently evolved sister South African (e. g., Cape and Pachycaul) subclades. The Cape and Pachycaul subclades diversified in the east of the Cape Peninsula in the mid Miocene, in an area with complex geomorphology and climate, where the fynbos, thicket, succulent karoo and forest biomes meet.



Diversification out of forest is associated with major shifts in morphology of the perennial tuber (specifically an increase in size and orientation which presumably led them to become pachycaul) and rotation of stem (from twining to non-twining). The iconic elephant's foot morphology, observed in grasslands and thicket biomes, where its corky bark may offer protection against fire and herbivory, evolved since mid Miocene. A shift in pollination trait is observed within the forest, but entry into open habitat does not show association with reproductive morphology, except in the seed wing, which has switched from winged all round the seed margin to just at the base or at the apex of it, or has been even replaced by an elaiosome.
African Centre for DNA Barcoding, Department of Botany & Plant Biotechnology, University of Johannesburg, PO Box 524, Auckland Park, Johannesburg, Gauteng, 2006, South Africa.|Royal Botanic Gardens, Kew, Richmond, Surrey, TW9 3AE, UK.
Olivier
O
Maurin
Department of Biological Sciences, University of Cape Town, Rondebosch, Western Cape, 7701, South Africa. muthama.muasya@uct.ac.za.
A Muthama
AM
Muasya
Departamento de Ciencias Agrarias y del Medio Natural, Escuela Politécnica Superior de Huesca, Universidad de Zaragoza, Ctra. Cuarte km 1, Huesca, 22071, Spain.|Institute of Biology, Tomsk State University, 36 Lenin Avenue, Tomsk, 634050, Russia.
Pilar
P
Catalan
African Centre for DNA Barcoding, Department of Botany & Plant Biotechnology, University of Johannesburg, PO Box 524, Auckland Park, Johannesburg, Gauteng, 2006, South Africa.
Eugene Z
EZ
Shongwe
Departamento de Biología Vegetal y Ecología, Facultad de Biología, Universidad de Sevilla, Av. Reina Mercedes s/n, Sevilla, 41012, Spain.|Institut Méditerranéen de Biodiversité et d'Ecologie marine et continentale (IMBE), Aix Marseille Université, Chemin de la Batterie des Lions, Marseille, 13007, France.
Juan
J
Viruel
Royal Botanic Gardens, Kew, Richmond, Surrey, TW9 3AE, UK.
Paul
P
Wilkin
African Centre for DNA Barcoding, Department of Botany & Plant Biotechnology, University of Johannesburg, PO Box 524, Auckland Park, Johannesburg, Gauteng, 2006, South Africa.
Michelle
M
van der Bank
D000349:Africa; D000818:Animals; D002980:Climate; D027742:Dioscorea / Q000033:anatomy & histology* / Q000145:classification / Q000502:physiology; D027743:Dioscoreaceae / Q000033:anatomy & histology* / Q000145:classification / Q000502:physiology; D017753:Ecosystem; D010802:Phylogeny; D018515:Plant Leaves / Q000033:anatomy & histology*
Biogeography; Dioscoreales; Fire adaptation; Habitat transition; Pachycaul; Southern Africa; Yams; “elephant’s foot”