cac•tus
(kăk′təs)
Plural cacti (kăk′tī′) or cactuses
Any of various plants that have thick, leafless, often spiny stems and grow in hot, dry places, chiefly in North and South America. Photosynthesis takes place in the stems of cacti, as the leaves have evolved into narrow spines toprevent water loss. Some kinds of cacti have brightly colored flowers and edible fruit.
Did You Know? The 2,000 species of cacti are known for living in extremely dry climates, such as the American Southwest. Cacti are excellent at conserving water. Their leaves are sharp spines, which have been known to cause great pain to animals interested in eating them. The spines also help the plant gather scarce water. Water vapor in theair condenses on the spines and then drips to the ground, where it is taken up by the roots. The roots are shallow and widely spread out to take advantage of this condensation and the rare desert rain showers. A cactus can be between 80 and 90 percent water, and its thick walls keep its water from evaporating. In fact, a cactus can be a thousand times better at conserving water than a different kind of plant of the same weight.