Which plants have which types of defense?.The varieties of phytochemical defenses in plants are so numerous that many questions about them remain unanswered, including: Many of these poisonous compounds also have important medicinal benefits.

Many of the known plant defense compounds primarily defend against consumption by insects, though other animals, including humans, that consume such plants may also experience negative effects, ranging from mild discomfort to death. Tannin, for example, is a defensive compound that emerged relatively early in the evolutionary history of plants, while more complex molecules such as polyacetylenes are found in younger groups of plants such as the Asterales. Over millennia, through the process of natural selection, plants have evolved the means to produce a vast and complicated array of chemical compounds to deter herbivores. Some plants have physical defenses such as thorns, spines and prickles, but by far the most common type of protection is chemical. Plants cannot move to escape their predators, so they must have other means of protecting themselves from herbivorous animals. The toxins in poisonous plants affect herbivores, and deter them from consuming the plants. Plants that produce toxins and/or causes irritation on contact are referred to as poisonous plants.

Australia, 1907: Cattlemen survey 700 cattle that were killed overnight by poisonous plants.

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