Speciation in Linaria subsect. Versicolores (Plantaginaceae, Antirrhineae) across the edaphic islands and barriers of the Algarve (Portugal)

Background and aims – The detection on the citizen science platform iNaturalist of an undescribed Linaria from the Monchique Igneous Complex (southwestern Portugal) prompted a reappraisal of the Iberian clade of L. subsect. Versicolores in the Algarve, in relation to the region’s complex geological diversity. Material and methods – The new species hypothesis was investigated using an integrative approach, combining phylogenomics based on genotyping-by-sequencing (GBS) data with a near-comprehensive revision of herbarium material and citizen science data of L. subsect. Versicolores from the Algarve. Geomorphogroups were identified based on geospatial analysis of distribution records and geological maps. Key results – Linaria alfercensis sp. nov. is part of a newly recognised, fully supported subclade endemic to the Algarve, together with L. algarviana and L. bimaculata . The new species is mostly confined to soils derived from nepheline syenites on the southern slopes of Serra da Picota, being preliminarily red-listed as Endangered. The other two members of the Algarvian subclade are near-endemic to the ‘Plio-Pleistocene sand archipelago’ of the Algarve. Two geomorphogroups of L. algarviana were identified, and the Albufeira and Cacela Gaps mostly define the western and eastern limits of the range of L. bimaculata , respectively. Geomorphogroups of L. spartea occur on Quaternary sands, the Triassic Silves Sandstone Line and some shales of the South Portuguese Zone. Linaria cf. viscosa is possibly confined to the aeolian sands of the Guadiana river mouth. Conclusion – The Iberian clade of Linaria subsect. Versicolores includes at least ten species. In the Algarve, limestone and other basic rocks, along with fine sands, shales, and greywackes, appear to function as edaphic barriers for this clade, while sandstone and coarse sand basins, igneous rocks, and aeolian sand plains represent edaphic habitat islands. This distribution pattern, associated with shifts in corolla colour and shape, denotes the role of geographical isolation and inferred edaphic specialisation in cladogenesis within L. subsect. Versicolores.