Systematics, taxonomy and biogeography of three new Asian genera of Brassicaceae tribe Arabideae: An ancient distribution circle around the Asian high mountains

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Abstract
Based on extensive molecular studies and critical evaluation of morphology, tribe Arabideae has recently been split into two tribes with the newly introduced tribe Stevenieae sister to the remaining members of tribe Arabideae. Tribe Stevenieae includes 11 species belonging to Pseudoturritis (1 sp.), Macropodium (2 spp.), and Stevenia (8 spp.). Tribe Arabideae includes about 488 species in 17 genera, and its taxonomy is highly affected by the previous para­ and polyphyletic circumscription of Arabis. Here we segregate three morphologically similar but phylogenetically distinct new genera, Scapiarabis, Borodiniopsis, and Sinoarabis from Arabis (tribe Arabideae) and provide keys to the genera of Arabideae as currently delimited and to the four species of Scapiarabis. Four new combinations in Scapiarabis (S. ariana, S. karategina, S. popovii, S. saxícola), one in Borodiniopsis (B. alaschanica), and one in Sinoarabis (S. setosifolia) are proposed. Arabis kamelinii and A. kokanika are reduced to synonymy of Scapiarabis ariana and S. saxicola, respectively. It is shown that Scapiarabis forms a clade with the monotypic genera Botschantzevia, Arcyosperma, Parryodes, and Borodiniopsis. Biogeographically the whole clade forms a circle around the Asian high mountain system, which is interrupted and separated by genetically distinct members of the sister clade that includes Baimashania, Pseudodraba and Sinoarabis. The whole biogeographic scenario predates the Pleistocene, and the genera are of Pliocene origin.

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