Phylogenetic, cytogenetic and morphological evidences are critical for recognizing a new genus: Valdesiana, an Iberian intergeneric allopolyploid between Schenkia and Exaculum

Abstract

The present taxonomic status of Schenkia elegans, endemism recently described in the Iberian Peninsula, and its relationship with the sympatric and the nearest morphological species Schenkia spicata and Exaculum pusillum is revaluated. Different kinds of evidence based on plant morphology, ploidy estimation by flow cytometry, karyotype characterisation, and phylogenetic data have been analysed. Two maternally inherited plastid DNA regions (trnL intron and trnL-F spacer) and biparentally inherited nuclear ribosomal DNA sequence region (nrDNA ITS) have been used. Comparative multivariate analyses show an intermediate morphology of the S. elegans plants between the other two species studied. Flow cytometry and karyotype analyses in S. elegans point to an allopolyploid origin, with the latter constituted by a mixture of those of the diploids S. spicata and E. pusillum. Phylogenetic analyses based on plastid and nuclear DNA regions cluster S. elegans in two different clades, those of S. spicata and E. pusillum, suggesting a possible hybrid origin of S. elegans between both species, acting as maternal or paternal progenitors. In consequence, taking in consideration the taxonomic relationships among genera (Exaculum, Schenkia and the closely related genus Zeltnera found in America), a monotypic genus Valdesiana gen. nov. is proposed to accommodate the allopolyploid species, combined as V. elegans, for which immediate conservation measures must be evaluated.