Morphological and genetic variation of highly endangered Bromus species and the status of these Neolithic weeds in Central Europe

Many Central European weeds were introduced in conjunction with increasing agricultural activities during the Neolithic period. Others likely originated in situ during crop domestication and selection. Among the European weeds occurring primarily in cereal fields are three tetraploid members of the genus Bromus (Poaceae), Bromus secalinus L. associated with rye (Secale cereale), and B. grossus Desf. ex DC. and B. bromoideus (Lej.) Crép. both occurring with spelt (Triticum aestivum spp. spelta) and other winter cereals. All three species may have had their diploid ancestors in the Near and Middle East, but have apparently evolved in Europe. Bromus grossus and B. bromoideus are highly endangered and the former is designated as a European Union Flora–Fauna Habitat Directive target species, while the latter is extinct in the wild. In contrast B. secalinus has successfully spread worldwide. In this study, we compared morphological and genetic variation among the three species to clarify morphological uncertainties and their genetic distinctiveness. It is shown that B. bromoideus has evolved from within the B. grossus gene pool. It has been extirpated from the wild and is now only cultivated in a few botanical gardens, such as at Meise and Heidelberg. In addition we also hypothesize that B. secalinus evolved from B. grossus.