A foxtail is a spikelet or spikelet cluster of a grass, that serves to disperse its seeds as a unit. Thus, the foxtail is a type of diaspore or plant dispersal unit. Some grasses that produce a foxtail are themselves called foxtail, also  spear grass .ot all of these are hazardous; most of the hazardous ones are in the genus Hordeum, and are also called wild barley. Grasses known as foxtails include: 1  Alopecurus (foxtail grasses-the scientific name literally means fox tail). 2  Bromus madritensis (foxtail brome).