Variation in Cnidoscolus texanus in relation to herbivory.

Twelve Oklahoma populations of Cnidoscolus texanus were investigated for morphological variation between and within populations, and between site classes with contrasting histories of use by domesticated livestock. Characters scored were numbers of stinging hairs on petioles and midribs, and depth of leaf lobing. Leaf lobing was not significantly variable within or among populations or grazing categories. Stinging hair numbers showed significant differences within and among populations. Petiole stinging hairs were more numberous in heavily grazed sites, suggesting population differentiation in response to the selective pressures of herbivory.