Delineation, taxonomy and phylogenetic relationships of the genus Krascheninnikovia (Amaranthaceae subtribe Axyridinae).

Morphological, morphometric and molecular phylogenetic studies in the Eurasian/North American genus Krascheninnikovia suggest to synonymise all previously described taxa of this genus under the single species K. ceratoides. Krascheninnikovia ceratoides comprises two subspecies: the North American subsp. lanata, comb. nov., and the Eurasian subsp. ceratoides. The subspecies ceratoides comprises in addition to the traditional K. ceratoides also K. arborescens, K. compacta, K. eversmanniana, K. intramongolica, K. lenensis and K. pungens. Specimens sampled from a single, large population of subsp. ceratoides in western Mongolia showed extreme inter-individual variation, which encompasses almost any attribute previously considered to separate the different Eurasian species. Molecular phylogenetic analysis of the nuclear ribosomal ITS1-5.8S gene-ITS2 DNA revealed the genus Krascheninnikovic, to be sister to the largely Asian genera Axyris and Ceratocarpus, all of which are characterised by the presence of stellate hairs. Nomenclaturally, subtribe Axyridinae, nom. nov., is proposed to cover this group in order to replace the illegitimate name Eurotiinae. The position of the North American genus Grayia, within or outside the Axyridinae, remains unsettled. Grayia is sister to Krascheninnikovia, Axyris and Ceratocarpus in the molecular phylogeny, but has no clearly stellate hairs, Its hairs appear intermediate between uniseriate and candelabra hairs and might be the precursor of stellate hairs. The adaptive significance of the different trichomes, life form evolution and biogeographical patterns are briefly discussed. [ABSTRACT FROM AUTHOR]