Aposematic (warning) coloration associated with thorns in higher plants

Aposematic coloration, a well-known phenomenon in animals, has been given l ittle attention in plants. Here I discuss two types of conspicuousness of t horns which are typical of many plant species: (1) colorful thorns, and (2) white spots, or white and colorful stripes, associated with thorns in leav es and stems. Both types of aposematic coloration predominate the spine sys tem of taxa rich with spiny species-Cacti, the genera Agave, Aloe and Eupho rbia. The phenomena have been recorded here in over a thousand species orig inating in several continents of both the Old and New World. I propose that this is a case of vegetal aposematic coloration analogous to such colorati on of poisonous animals, and which communicates between plants and herbivor es. (C) 2001 Academic Press.