ABSTRACT
Poisonous plants often are the least understood and most misrepresented class of plants on rangelands. Most poisonous plants are forbs, and C. W. Cook indicated that most range managers treat forbs as weeds or least desirable plants. This chapter aims to develop a comprehensive list of poisonous plants by occurrence in different seral stages or with differential responses to grazing. It shows that most lists either ignored poisonous plants, gave them low species composition values, or classified them as increasers, invaders, or undesirable, often without regard to their true ecological status. Some understanding of how the poisonous properties of plants may have evolved is important to understanding the role of poisonous plants in natural communities. Poisonous species might gain a competitive advantage if they were so toxic that consumption by an herbivore resulted in death or lowered fitness of the animal in terms of growth rate or fecundity.
