Stellaria ruderalis, a new species in the Stellaria media group from central Europe

A new allotetraploid species in the Stellaria media group, S. ruderalis M. Lepší, P. Lepší, Z. Kaplan & P. Koutecký, which is possibly of hybridogenous origin between S. pallida and S. neglecta, is distinguished and described based on a biosystematic revision of the S. media group. A suite of biosystematic techniques, including molecular (internal transcribed spacer sequencing), karyological (chromosome counting, flow cytometry), multivariate morphometrics and phenological observations, was used to assess the variation in this species group and determine the taxonomic status of the species. All the methods employed produced similar results and supported the delimitation of four species within the Stellaria media group in central Europe: Stellaria ruderalis (2n = 4x = 44), S. pallida (2n = 2x = 22), S. neglecta (2n = 2x = 22) and S. media s. str. (2n = 4x = 40). Stellaria ruderalis is a winter annual growing mainly in disturbed ruderal open or semi-open communities. This species’ broad ecological amplitude allows it to commonly co-occur with its three related species. It is probably a widespread species in southern and central Europe. It is currently spreading in the northern part of central Europe. Photographs of the type specimen and individuals of the new species in situ are presented. Scanning electron micrographs of seeds, microphotographs of seeds and mitotic chromosome spreads and a key for the identification of all four species are provided.