Revisiting monophyly in Haworthia Duval (Asphodelaceae): Incongruence, hybridization and contemporary speciation

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Abstract:

Molecular phylogenetic reconstructions have indicated that Haworthia is not monophyletic. Here we show, using considerably expanded datasets of both chloroplast (trnL-trnF and psbA-trnH intergenic spacers) and nuclear (ITS1) markers that the issue of a polyphyletic Haworthia is more complicated than previously reported. Both parsimony and bayesian analyses of cpDNA and ITS1 produced poorly resolved phylogenies, with little or no support for deeper nodes. Species of Haworthia are placed in three of the four main lineages in the cpDNA phylogeny, while in the ITS1 phylogeny Haworthia species were placed in two of the four main lineages retrieved. The cpDNA phylogeny was incongruent with that obtained from the ITS1 data, and the topology of the combined dataset reflected that obtained from the ITS1 dataset. As species of H. subg. Hexangulares and subg. Robustipedunculares have been reportedly involved in intergeneric hybridizations with other Alooideae, it is postulated that a history of ancient hybridization may account for a polyphyletic Haworthia. Hybridization is also ongoing between species within H. subg. Haworthia, and may be responsible for results indicating that some species in this subgenus are not monophyletic. This hybridization may be facilitated by the lack of effective reproductive barriers. We hypothesize that Haworthia is undergoing a contemporary and explosive radiation in southern Africa, driven in part by local adaptation to relatively fine-grained ecological heterogeneity of soils and microclimate.

Keywords: CONTEMPORARY RADIATION; HAWORTHIA; HYBRIDIZATION; INCONGRUENCE; ITS1; NON-MONOPHYLY; PSBA-TRNH; TRNL-TRNF

Document Type: Research Article

Affiliations: 1: Department of Botany, Nelson Mandela Metropolitan University, P.O. Box 77000, Port Elizabeth, 6031, South Africa; Geography, School of Environmental Science, Westville Campus, University of KwaZulu-Natal, Private Bag X54001, Durban, 4000 2: Molecular Ecology & Systematics Group, Department of Botany, Rhodes University, Grahamstown, 6140, South Africa 3: Department of Botany, Nelson Mandela Metropolitan University, P.O. Box 77000, Port Elizabeth, 6031, South Africa

Publication date: August 1, 2011

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