Plants have developed many defenses against herbivore, varying from the complex to the simple. Coconut palms and many oak nut trees preserve their roots by surrounding them in layers of woody or tough tissue which are hard to get through.
Physical defenses, which are mostly constitutive lead more to the apparent side; for example, thorns and ridges have developed in several groups as protection from herbivores.
Chemical defenses may be constitutive or persuaded, indicating that they develop or strengthen when herbivore is identified by the plant. Many elements are simply strong tasting, such as the lubricants which generate their heat or the sour tasting tannin present in several plant families.
