Molecular systematics, biogeography and dating of the tribe Haemantheae (Amaryllidaceae) and the phylogeography of Clivia
The African tribe Haemantheae, belonging to the monocotyledonous family Amaryllidaceae, comprises six genera (Gethyllis, Apodolirion, Haemanthus, Scadoxus, Clivia and Cryptostephanus) with ca. 90 species. A phylogenetic hypothesis for the Haemantheae is presented as a basis for an enquiry into the generic and species relationships within the tribe. DNA sequence data from five plastid regions: the rpoB-trnC intergenic spacer, trnL intron, trnL-F intergenic spacer, the rps16 intron, the psbA-trnH intergenic spacer and internal transcribed spacer region (ITS) have been collected and analysed for 62 taxa within this tribe using two outgroups within Amaryllidaceae. Combined parsimony and Bayesian analyses of the five plastid and one nuclear region indicated that Scadoxus and Haemanthus are monophyletic and resolved as sister clades to one another. The summer rainfall group of species within the genus Haemanthus is monophyletic. The genus Apodolirion is embedded within Gethyllis as has been previously suggested on morphological grounds. Both Clivia and Cryptostephanus resolved as monophyletic groups with Cryptostephanus placed as sister to Clivia. Character optimizations of 15 morphological characters were carried out and optimization of the character ‘anther number’ revealed the strongest evidence so far for not recognising the informally recognized Gethyllis ‘villosa’ group. Biogeographic analyses using the divergence/vicariance (DIVA) method were inconclusive in determining the ancestral node of Haemantheae as the phytogeographic areas occupied by the taxa were too widespread. Two methods, non parametric rate smoothing (NPRS) and a Bayesian method (implemented in BEAST) were used in the assessment of age estimates and divergence times within the Haemantheae. Due to a lack of fossil record for this group, a calibration point from Wikström et al. (2001) of 33 Ma was used, based on the split of Haemantheae and Hippeastreae. Results indicate a rapid diversification for the winter rainfall lineages of Haemanthus at around 5 Ma coinciding with the late Miocene/Pliocene and the aridification and formation of a Mediterranean-type climate in southwestern Africa. In contrast, Gethyllis reflects a gradual diversification from 20-8Ma before the onset of aridification and the establishment of the Mediterranean-type climate. Analyses of the Clivia populations reveal occasional haplotype sharing between Clivia species in those parts of the distribution range where they are sympatric. The interconnectedness of C. gardenii and C. robusta brings into question the recognition of these two entities as discrete species.
Networked Digital Library of Theses and Dissertations