Abstract
Chenopodium rugosum was described by Aellen in 1928, based on a specimen collected in Siberia by Arnell and deposited in the US Herbarium. For a long time, this Aellen’s name was forgotten or ignored by the researchers, mainly because of the uncertain identity of that taxon and unavailability of its type. We report here the holotype of C. rugosum recently found in US. The specimen was collected in 1876 by Arnell in Verkhneimbatsk (Turukhanskiy District, Krasnoyarskiy Kray, Russia) at the confluence of the Verkhniy Imbach River and the Yenisei River. Taxonomically the holotype of C. rugosum clearly belongs to the C. album aggregate and morphologically seems to be similar to C. striatiforme, a tetraploid “microspecies” related to C. betaceum. However, C. rugosum might be also a hexaploid close to C. album s. str. From a nomenclatural viewpoint, the name C. rugosum by Aellen is illegitimate, being a later homonym of the long-forgotten earlier name C. rugosum validated by Rafinesque in 1830 for some forms of C. ambrosioides (now recognized in Dysphania). Taxonomic and nomenclatural comments are provided on these names.