Cactus
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A cactus (plural: cacti) is a member of the plant family Cactaceae, native to the Americas (with one exception, Rhipsalis baccifera, which is native to parts of the Old World). They are often used as ornamental plants, and some are also crop plants for fodder, forage, fruits, cochineal, and other uses. Numerous species have been used since ancient times by indigenous peoples for their psychedelic effects. Cacti are part of the plant order Caryophyllales, which also includes members like beets, gypsophila, spinach, amaranth, tumbleweeds, carnations, rhubarb, buckwheat, plumbago, bougainvillea, chickweed and knotgrass. Cacti are unusual and distinctive plants, which are adapted to extremely arid and/or semi-arid hot environments, as well as tropical environments as epiphytes or hemi-epiphytes. They show a wide range of anatomical and physiological
features which conserve water. Their stems have adapted to become photosynthetic and succulent, while the leaves have become the spines for which cacti are well known. Cacti come in a wide range of shapes and sizes. The tallest is Pachycereus pringlei, with a maximum recorded height of 19.2 m, and the smallest is Blossfeldia liliputiana, only about 1 cm diameter at maturity. Cactus flowers are large, and like the spines and branches arise from areoles. Cacti are perennial and grow as trees, shrubs, or vines. Most species are terrestrial, but there are also many epiphytic species, especially in the tribes Rhipsalideae and Hylocereeae. In most species, except for the sub-family Pereskioideae (see image), the leaves are greatly or entirely reduced. The leaves may also be tiny and deciduous as can be seen on new shoots of Opuntia. Spines grown by the cacti are actually modified leaves; the stems (the green "pads" of many cacti) have also evolved to photosynthesize. The study of when spines grow and how they can be used to tell the cactus' age is called acanthochronology. The flowers, mostly radially symmetrical and bisexual, bloom either by day or by night, depending on the species. Their shape varies from tube-like through bell-like to wheel-shaped, and their size from 0.2 to 15–30 centimetres. Most of them have numerous sepals (from 5 to 50 or more), and change form from outside to inside, from bracts to petals. They have stamens in great numbers (from 50 to 1,500, rarely fewer). Nearly all species of cacti have a bitter mucilaginous sap contained within them. The berry-like fruits