A cactus is any member of the spine plant family Cactaceae, native to the Americas. They are often used as ornamental plants, but some are also crop plants. Cacti are part of the plant order Caryophyllales, which also includes members like beets, baby’s breath, spinach, amaranth, tumbleweeds, carnations, rhubarb, buckwheat, plumbago, bougainvillea, chickweed and knotgrass.
The cacti are spine plants that grow either as trees, shrubs or in the form of ground cover. Most species grow on the ground, but there is also a whole range of epiphytic species. In most species, except for the sub-family of the Pereskioideae, the leaves are greatly or entirely reduced. The flowers, mostly radially symmetrical and hermaphrodite, bloom either by day or by night, depending on species. Their shape varies from tube-like through bell-like to wheel-shaped, and their size from 0.2 to 15-30 centimeters.
Most of them have numerous sepals, and change form from outside to inside, from bracts to petals. They have stamens in great numbers. Nearly all species of cacti have a bitter sometimes milky sap contained within them. The berry-like fruits may contain few, but mostly many, seeds, which can be between 0.4 and 12 mm long.
The life of a cactus is seldom longer than 300 years, and there are cacti, which live only 25 years. The Saguaro cactus grows to a height of up to 15 meters, but in its first ten years, it grows only 10 centimeters. The “mother-in-law’s cushion” reaches a height of 2.5 meters and a diameter of 1 meter and - at least on the Canaries - is already capable of flowering after 6 years. The diameter of cactus flowers ranges from 5 to 30 cm; the colors are often conspicuous and spectacular.