Cactus: North American Opuntia, Cylindropuntia, Grusonia etc..
The Opuntia family of cactus include plants that most people are familiar with, such as the Prickly Pears, and the Chollas. These cacti have some unique features that other cacti don’t have, such as true leaves on the new growths, and a type of spine called glochids, which are very small, fine spines that readily detach if a human or animal brushes against them. The spines and glochids are also barbed which is thought to aid the plant in vegetative reproduction. When the segment gets hooked onto an animal, it detaches and is carried away to possibly start a new plant in another location.
The Opuntia can be found as far north as Canada, and down through the US and Mexico, then down into South America. Some species are considered invasive in other parts of the world such as Africa, Australia, and Mediterranean areas of Europe.
Echeveria is a large genus of succulent plant in the family Crassulaceae. Their natural habitat is often cliff faces, and can be found from Mexico, Central America, down into South America.
These plants form rosettes of often brightly colored leaves, and are very popular with collectors. The numerous small flowers form on stalks that arise from near the center of the rosette. Most people grow them for the form of the plant rather than for the flowers though.
Photos: Prickly Pear and Cholla from the Mojave desert, Cholla flower, and Echeveria agavoides ‘Ebony’