Hordeum murinum, “Wall barley”, “Mausegerste”, or “Kruipertje” is indigenous to Europe. It is a weed of waste ground and is a common grass around vacant buildings, harbours, railways, grain dispersal areas, factory yards, playgrounds etc. Its mode of dissemination and the ability to survive under poor soil conditions enables it to become established quickly on abandoned or disturbed areas. Therefore, although it probably does not originate here, Holland with a network of canals, rivers, and roads has many ideal sites for introduction and the grass is common to most parts of the country (Jansen, 1951). The species was first named by Linnaeus in Species Plantarum 1753. Several adequate descriptions have since been published (Jansen 1951; Hubbard 1954; or see any other European Flora). Possibly because of conditions under which the plants grow and also because of some innate genetical variability, many morphological forms occur—in height alone the plants may vary from a few cm to almost a meter. The extremes in form have caused some difficulties in classification and at present there are differing opinions as to whether specific or subspecific rank should be used for certain taxa in the genus Hordeum. The disorder has been heightened because the morphological features used to delineate species are small and variable characters that often overlap. For example, H. leporinum Link was described as a robust plant with large lateral spikelets. The size of the lateral spikelets or the ratio of the laterals to the median has indeed been used as a key for separating this species from H. murinum: in murinum the median spikelet is longer than the laterals, in leporinum the laterals are longer. Problems in classification immediately arise when plants with spikelets of equal size occur. Another species of this group, usually referred to as the murinum complex, has been named H. glaucum Steudel. This species was erroneously named H. stebbinsii (Covas 1949) but Stebbins himself agrees (personal communication) that the correct name is glaucum.