Flowers

All cacti flower, although some more readily than others. Some species reach flowering size in a couple of years from seed, whereas others, especially the large treelike species, may take decades to reach flowering size.

Cactus flowers come in a variety of shapes, colors and sizes; each flower type attracts different pollinators, such as nocturnal bats and moths, bees , beetles and hummingbirds.
There are no poisonous species, although several contain distasteful chemicals that are thought to inhibit predestination by animals, insects and perhaps microbes.

There are no known early fossil cacti oldest fragments date back only 22 000 yrs, so all hypotheses as to their evolution have to be inferred from study of the anatomy, distribution, chemistry and genetics of living species.

The cactus family is essentially New World in distribution, ranging from the Peace River Lowland of northern British Columbia to Patagonia in southern Argentina and Chile.

The only cacti that occur naturally outside the Americas are 3 subspecies of parts of Africa, islands off the southeast coast of Africa and Sri Lanka.

see photo :

http://nature.desktopnexus.com/wallpaper/1430241/