Taxonomy and evolutionary history of Alyssum montanum (Brassicaceae) and related taxa in southwestern Europe and Morocco: Diversification driven by polyploidy, geographic and ecological isolation

Abstract

The Alyssum montanum–A. repens polyploid complex is a group of related perennial taxa with a diversity centre in the European (Sub)Mediterranean, controversial taxonomic treatments, and a poorly known evolutionary history. In the present study, morphological, ploidy level and genetic (AFLPs and chloroplast DNA sequences) data were collected to address the taxonomy and evolution of a sublineage of this complex distributed in southwestern Europe and Morocco. As a result, a new taxonomic treatment, differing substantially from recent concepts, is presented, including an identification key, synonymy and typifications. The recognition of several previously described but recently not accepted endemics is favoured (A. flexicaule, A. orophilum, A. rhodanense), whereas the existence of southern Iberian endemics is not supported. Most of the Iberian Peninsula is occupied by a single species for which the name A. fastigiatum is applicable. Populations from the summit areas of the Pyrenees represent a separate species, which is described here as A. cacuminum. Populations from coastal sand dunes in the Basque country (Bay of Biscay) and Galicia, recently recognised as two subspecies of A. loiseleurii, are elevated to species rank according to their genetic and morphological divergence. Alyssum atlanticum is resolved as a species confined to northern Africa and not reaching southern Spain. The distribution of A. montanum in a strict sense is much more restricted than previously reported, being delimited by the Pyrenees in the south, and the Alps in the northeast. The species complex studied here is composed of several polyploid stenoendemics confined to different mountain ranges or specific lowland habitats, and a few relatively widely distributed species. We infer that hybridisation and polyploidisation events, along with ecological and geographic isolation, have stimulated speciation in this complex. Hypotheses about the origin and evolutionary history of the species are discussed.

Polyphyletic Alyssum cuneifolium (Brassicaceae) revisited: Morphological and genome size differentiation of recently recognized allopatric taxa

“…The population of A. spruneri growing on Mt Smolikas is tetraploid (2 x and 4 x were recorded for other populations of this species in Greece and the central Balkans, Španiel et al, ). The population of A. fastigiatum from the Tozal de Guara is diploid (2 x and 4 x have been recorded in other populations of this species, Zozomová‐Lihová et al, ). Contrasting data have been published for A. cuneifolium : Manton () reported diploids (2 n = 16, the locality not given) whereas Küpfer () reported hexaploids (2 n = 48, Monti Sibillini in central Italy, but see the Discussion).…”

“…losanum ) was not available for this study. Alpine populations of A. fastigiatum from Sierra Nevada and A. orophilum from the Western Alps (previously assigned to A. cuneifolium probably only by Baumgartner, ) were not analysed here either, as they mostly inhabit places with denser vegetation among rocks and alpine bushes (different habitats than those occupied by typical alpine scree taxa/populations) and are morphologically clearly different (as demonstrated by Zozomová‐Lihová et al, ).…”

“…The interpretation of the results was based on ploidy levels and chromosome counts obtained from reference plants of other species of the A. montanum‐A. repens complex in previous studies (Španiel et al, , ; Zozomová‐Lihová et al, ). This approach is sufficiently reliable due to non‐overlapping ranges of genome size among diploids (0.53–0.89), tetraploids (1.17–1.65) and hexaploids (1.80–2.22) of all hitherto investigated European species of the A. montanum‐A.…”

“…repens species complex from lowland to montane sites, the alpine populations from the aforesaid isolated mountain ranges share similar morphology: they have a typical procumbent habit, flexuous stems, relatively wide petals and congested fruit racemes. The two recently published molecular studies (Zozomová‐Lihová et al, ; Španiel et al, ), however, have revealed that these allopatric populations traditionally assigned to A. cuneifolium are genetically clearly different and do not form a monophyletic group. Instead, they show higher genetic affinities to geographically closer, but morphologically differentiated, lower‐elevation members of the A. montanum‐A.…”

“…Three different ploidy levels have been reported for these alpine scree taxa and populations. Alyssum cacuminum is tetraploid, rarely hexaploid (Zozomová‐Lihová et al, ), A. flexicaule is hexaploid (Zozomová‐Lihová et al, ), and A. pirinicum is diploid (Anchev, ; Španiel et al, ). The population of A. spruneri growing on Mt Smolikas is tetraploid (2 x and 4 x were recorded for other populations of this species in Greece and the central Balkans, Španiel et al, ).…”