There are over 2000 species of cacti. The two major classifications are opuntias and cactoids.
The smallest cacti grow to about 1 cm thick and only a few cm high. The tallest can grow up to 1 m (3 feet) thick and 65 feet (20 m) tall. The largest can weigh up to 4800 lb (2180 kg) when filled with water.
Nearly all cacti are native to dry regions in the North and South Americas.
Cacti can be green, brownish-green, or blue in color.
The outside of a cactus is covered in a waxy substance which helps prevent water loss.
Cacti have spines that can be up to 6 inches long. They keep the protect the plant from animals and prevent water loss.
Certain species of cacti can live to 15 years, while others can live to 300 years.
Cactus water is drinkable. But certain cacti produce mescaline, which is a hallucinogen.
Cactus roots are very short, but grow to be quite wide - up to 7 feet (2.1 m).
Some cacti can produce flowers. These can be red, pink, orange, white, or blue.