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Hybridization is an important evolutionary factor in the diversification of many plant and animal species. Of particular interest is that historical hybridization resulting in the origin of new species or introgressants has occurred between species now geographically separated by great distances. Here, we report that Senecio massaicus, a tetraploid species native to Morocco and the Canary Islands, contains genetic material of two distinct, geographically separated lineages: a Mediterranean lineage and a mainly southern African lineage. A time-calibrated internal transcribed spacer phylogeny indicates that the hybridization event took place up to 6.18 Ma. Because the southern African lineage has never been recorded from Morocco or the Canary Islands, we hypothesize that it reached this area in the distant past, but never became permanently established. Interestingly, the southern African lineage includes S. inaequidens, a highly invasive species that has recently become widespread throughout Europe and was introduced at the end of the 19th century as a 'wool alien'. Our results suggest that this more recent invasion of Europe by S. inaequidens represents the second arrival of this lineage into the region.

Tamarix usneoides (Tamaricaceae) is a species native to southern Africa where it is currently being used in the mines for phytoremediation. Tamarix aphylla, Tamarix ramosissima, Tamarix chinensis, and Tamarix parviflora have been reported as exotic species in South Africa, with T. ramosissima declared invasive. The alien invasive T. ramosissima is hypothesized to be hybridizing with the indigenous T. usneoides. Accurate identification of Tamarix is of great importance in southern Africa because of the invasive potential of T. ramosissima and also the potential usefulness of T. usneoides. In this study, nuclear DNA sequence markers (ITS1 and ITS2 regions), together with the plastid marker trnS-trnG, are used to identify the genetic distinctiveness of Tamarix species and their putative hybrids. Phylogenies based on the ITS and trnS-trnG regions revealed that the indigenous T. usneoides is genetically distinct from the exotic species, which, however, could not clearly be separated from their closely related hybrids. The lack of congruence (p N 0.0001) between the ITS and trnS-trnG phylogenies suggests that there is high incidence of hybridization in Tamarix populations in South Africa. Importantly, molecular diagnosis of Tamarix was able to identify hybrids using polymorphisms and phylogenetic signals. Close to 45% of Tamarix genotypes were hybrids with more than 50% of them occurring on the mines. Spread of Tamarix hybrids in South Africa through phytoremediation could enhance invasiveness. Therefore, the outcome of this study will ensure that only pure indigenous T. usneoides is propagated for planting on the mines in South Africa and that a proper control measure for the alien invasive Tamarix is used. Interestingly, the molecular diagnosis of Tamarix species supported the preliminary morphological identification of the species using eight key characters. However, the molecular markers used were not informative enough to separate hybrids from their closely related parent species. Hybrids were more reliably identified using polymorphisms than morphological features.

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Evolutionary trends and phylogenetic relationships in the Strelitziaceae (Zingiberales) were investigated using sequence data from ten plastid and two nuclear regions and a morphological dataset. The status of species of Strelitzia were evaluated in terms of the phylogenetic species concept. Relationships among the genera remain equivocal with two hypotheses emerging: (i) Strelitzia sister to a clade comprising Raivnala and Phenakospermum when indels are included, or (ii) Ravenala sister to the remainder of the Strelitziaceae when indels are excluded in/from the combined molecular and 'total evidence' analyses. Within Strelitzia, S. nicolai is sister to the rest of the genus, with S. alba sister to S. caudata. Strelitzia regirme is shown to be paraphyletic as S. júncea is nested within it, but more sampling at the population level is needed to confirm the taxonomic status of S. júncea. The highly localized and endangered Strelitzia alba is confirmed as a distinct species, as are S. caudata and S. nicolai, despite few morphological differences. Evolutionary trends are linked to changes in habitat and coevolution with pollinators. Climate change in southern Africa is thought to have restricted Strelitzia nicolai (or its ancestor) to the eastern coastal region, with subsequent allopatric speciatíon of S. alba and S. caudata, and relatively recent parapatric divergence of S. júncea from S. reginae. SYSTEMATIC BOTANY [Volume 37 MATERIALS AND METHODSTaxon Sampling-All seven currently recognized species comprising the three genera of the Strelitziaceae and two outgroup species, Orchidantha fimbriata and O. siamensis, were included in this study. Orchidantha N. E. Br., the single genus in the Lowiaceae (Lane 1955;Johansen 2005), was selected as the outgroup based on previous phylogenetic analyses. Lowiaceae has repeatedly been recovered as sister to the Strelitziaceae (Chase et al 2000; Solfis et al. 2000;Kress et al. 2001;Givnish et al. 2006;Soltis et al. 2007), with one exception where Lowiaceae was placed sister to remaining families of the Zingiberales, with Strelitziaceae comprising the next clade-diverging (Johansen 2005). Multiple exemplars (two individuals per species) were used for all Strelitzia species to test for monophyly. Appendix 1 lists the specimens with accession numbers and vouchers.Molecular Characters-Rapidly evolving intron and intergenic spacers were selected from ten plasfid regions, viz. matK -5'trnK, psbA-matK, psbB-psbH, Ycf6-trnC, rpL16 intron, rpoB-trnC, trnS-trnfM, triiY-trnE (Shaw et al. 2005), rpL32-trnt (Shaw et al. 2007), rpS16 (Levin et al. 2004), and two nuclear regions: the external transcribed spacer (ETS) region of ribosomal DNA and rpb2, the second intron of the second subunit of RNA polymerase II. A single accession for each member of the Strelitziaceae was sequenced for all ten plastid regions, and a second accession sequenced for three plastid regions, matK -5'trnK, rpS16 and the rpL16 intron (with the exception of R. madagascariensis and S. alba for the rpL16 intron), and the ...