Abstract
Habitats with alkaline edaphic substrates are often associated with plant speciation and diversification. The tribe Alysseae, in the family Brassicaceae, epitomizes this evolutionary trend. In this lineage, some genera, like Hormathophylla, can serve as a good case for testing the evolutionary framework. This genus is centered in the western Mediterranean. It grows on different substrates, but mostly on alkaline soils. It has been suggested that diversification in many lineages of the tribe Alysseae and in the genus Hormathophylla is linked to a tolerance for high levels of Mg+2 in xeric environments. In this study, we investigated the controversial phylogenetic placement of Hormathophylla in the tribe, the generic limits and the evolutionary relationships between the species using ribosomal and plastid DNA sequences. We also examined the putative association between the evolution of different ploidy levels, trichome morphology and the type of substrates. Our analyses demonstrated the monophyly of the genus Hormathophylla including all previously described species. Nuclear sequences revealed two lineages that differ in basic chromosome numbers (x = 7 and x = 8 or derived 11, 15) and in their trichome morphology. Contrasting results with plastid genes indicates more complex relationships between these two lineages involving recent hybridization processes. We also found an association between chloroplast haplotypes and substrate, especially in populations growing on dolomites. Finally, our dated phylogeny demonstrates that the origin of the genus took place in the mid-Miocene, during the establishment of temporal land bridges between the Tethys and Paratethys seas, with a later diversification during the upper Pliocene.
Highlights
According to the results of the expanded ITS data set (S1 Fig), which included a comprehensive sampling of DS1, the sister group of the genus Hormathophylla (0.91 PP; 61% BS) was composed of Acuston Raf., Alyssoides, Mill., Brachypus Ledeb., Clastopus Bunge ex Boiss., Degenia Hayek, Fibigia Medik., Irania Hadač & Chrtek, Lutzia Gand., Physoptychis Boiss., Pterygostemon V.V
Within haplogroup II, we find species that were always present on alkaline soils, with a particular predominance of dolomitic or calcodolomitic substrates (H. reverchonii, H. longicaulis, H. cadevalliana and H. lapeyrouseana), but all the individuals analyzed from populations living on serpentines (H. longicaulis) are in this group
The first corresponded to H. reverchonii individuals (1.00 PP; 97% BS), two more contained sequences from the southernmost populations of H. lapeyrouseana, and two more (0.99 PP; 88% BS and 1.00 PP; 72% BS) contained samples belonging to H. cadevalliana and H. longicaulis, with many of their sequences grouped as mixtures from both species (0.97 PP; 60% BS)
Summary
We sampled all the species that were previously assigned to Hormathophylla with an emphasis on the most taxonomically controversial taxa from the Baetic ranges (Table 1). Mey.) Boiss., respectively) because of their uncertain generic affinities and their possible relationship to Hormathophylla In this sense, the putative ascription of C. antiatlantica to Hormathophylla was informally suggested by Kupfer (in some annotated herbarium specimens, e.g. MA 121991) as well as by Maire, who highlighted its morphological similarity to H. cochleata and Alyssum sect. Voucher information with herbarium abbreviations according to Thiers [41] and GenBank numbers for all the accessions used are shown in Table 2 (from Hormathophylla genus) and Table 3 (rest of taxa used in the studies). One more data set (DS3) was used that was composed of plastid sequences (trnL-F, trnT-trnL and rpl32-trnl) sequenced in the case of the genus Hormathophylla and species from related genera Fibigia, Brachypus and Alyssoides. For cpDNA sequences, three regions were selected, according to the degree of polymorphism shown These sequences were: trnL-trnF, trnT-trnL and rpl32-trnL.
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