A morphological description is provided for Chenopodium ucrainicum Mosyakin & Mandák (Chenopodiaceae / Amaranthaceae sensu APG), a new species allied to C. suecicum and C. ficifolium. At present this new species is reliably known from several localities in Ukraine (three areas in Kyiv city, one in Kyiv Region, one in Rivne Region), but it is probably more widespread, or could be even alien in Eastern Europe. Comparison of our plants with other taxa [such as C. suecicum (incl. C. neumanii, etc.), C. ficifolium, several morphotypes of C. album, as well as plants known as C. borbasii, C. missouriense (sensu stricto and sensu auct. europ.), C. lobodontum, etc.], demonstrated that C. ucrainicum is morphologically different from all these known and named taxa. It is also a late-flowering and late-fruiting species: in Kyiv fruits/seeds normally develop during late September – early November. This significantly reduces the possibility of gene flow and therefore hybridization with closely related diploid species, like C. ficifolium or C. suecicum, which usually flower and produce fruits earlier, mainly in July–August to early September. It also suggests that the new taxon is well isolated from its congeners and indeed represents a good species, not just one of weakly differentiated morphotypes that are so numerous in the C. album aggregate. To help researchers in identifying C. ucrainicum in the field and in herbaria, original illustrations are provided in the article and the Electronic Supplement. These illustrations include scanned images of the holotype (one specimen representing parts of one plant mounted on four herbarium sheets), field photographs showing plants and their parts at different stages of their development, and photomicrographs of fruits/seeds. Cytological and molecular data of the research team of B. Mandák (research in progress, detailed results to be published separately) demonstrated that C. ucrainicum is a B-genome diploid indeed related to C. suecicum and C. ficifolium.
Supplementary Material. Electronic Supplement (Figures E1–E20, e1–e10) is available in the online version of this article.
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