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

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. OutgroupAloe plicatilis Haworthia II True Aloes Tree-like Aloes Haworthia I Haworthia subg. Haworthia (n = 13) Outgroup Haworthia II Tree-like Aloes Aloe plicatilis Haworthia I True AloesHaworthia subg. Haworthia (n = 4) Aloe ciliaris Aloe aristata Gasteria Haworthia subg. Hexangulares (n = 10) Haworthia subg. Haworthia (n = 2) Gasteria (n = 3) Aloe aristata (n = 2) Astrolaba spiralis (n = 2) Haworthia subg. Hexangulares (n = 18)

Molecular and morphological analysis of subfamily Alooideae (Asphodelaceae) and the inclusion ofChortolirioninAloe

“…Although the monophyly of the subfamily is no longer in question, this cannot be accepted for all of the genera. It has become increasingly clear that neither Aloe nor Haworthia are monophyletic as currently circumscribed (Treutlein & al., 2003a, b;Ramdhani & al., 2011). Our analysis of the combined plastid and nuclear DNA datasets (Fig.…”

“…PCR amplification was performed using the following programs: for rbcLa and trnH-psbA, pre-melt at 94°C for 3 min, denaturation at 94°C for 1 min, annealing at 48°C for 1 min, extension at 72°C for 1 min (for 28 cycles), followed by a final extension at 72°C for 7 min; for matK, the protocol consisted of pre-melt at 94°C for 1 min, denaturation at 94°C for 30 s, annealing at 50°C for 40 s, extension at 72°C for 40 s (for 35 cycles), and a final extension at 72°C for 5 min. We selected ITS1 for phylogeny reconstruction because of its value in previous studies in the subfamily (e.g., Treutlein & al., 2003a, b;Ramdhani & al., 2011) and also because it has been routinely used to infer phylogenetic relationships at various infrageneric levels in other plant groups (Hillis & Dixon, 1991;Baldwin & al., 1995;Small & al., 2004). A preliminary PCR amplification of Alooideae using ITS2 was unsuccessful.…”

“…Leptoaloe, and Lomatophyllum was firmly nested within another unresolved clade of Aloe. A later study by Ramdhani & al. (2011) addressed phylogenetic relationships in the genus Haworthia, analysing relationships among 26 species from all three subgenera (H. subg.…”

“…The last decade has seen the emergence of phylogenetic studies of nucleotide sequence data in assessing relationships within Alooideae (Adams & al., 2000;Chase & al., 2000;Treutlein & al., 2003a, b;Zonneveld & Van Jaarsveld, 2005;Ramdhani & al., 2011). Phylogenetic relationships in Asphodelaceae were first investigated by Chase & al.…”

“…Despite their shortcomings, most attempts at resolving relationships in Alooideae (e.g., Adams & al., 2000;Chase & al., 2000;Treutlein & al., 2003a, b;Zonneveld & Van Jaarsveld, 2005;Ramdhani & al., 2011) suggest that there is some degree of mismatch between current generic circumscriptions in the subfamily and available phylogenetic hypotheses. As yet, however, no adequately sampled or well-supported phylogenetic analysis exists on which to base an alternative classification.…”