Some notes on the Hordeum murinum complex in Belgium

Hordeum murinum subsp. murinum is a common archaeophyte in Belgium. A more southern subspecies, subsp. leporinum, is known since 1938 as a rare, ephemeral alien, mostly associated with the grain or wool industry. In the past decade, however, it has increasingly been recorded. In port areas in Antwerp and Ghent it has locally naturalized along railway tracks, on roadsides and rough ground. In addition, it is also found in similar habitats in urban areas. A third subspecies, subsp. glaucum, is also reported for the first time in Belgium, as a mere casual alien. The separation of these three taxa is not straightforward. Characters useful for their distinction are presented and all subspecies are illustrated as well.