目录:
仙人掌（仙人掌科），复数仙人掌或仙人掌，有近2000种139属的开花植物科（石竹科）。仙人掌在北美洲和南美洲的大部分地区都是本地人，从不列颠哥伦比亚省和艾伯塔省向南；其范围的最南端延伸到智利和阿根廷。墨西哥的物种数量和种类最多。唯一可能起源于旧世界的仙人掌是Rhipsalis属的成员，它们分布在东非，马达加斯加和斯里兰卡。尽管少数仙人掌物种生活在热带或亚热带地区，但大多数都生活在干旱地区并且非常适合干旱地区。另请参阅仙人掌科植物列表。
石竹叶科：仙人掌科
仙人掌是好奇的，通常是棘手的（多刺的），多汁的茎状植物，构成仙人掌科，具有一定的特征并且适应性强
物理特性
仙人掌是多年生的肉质植物。仙人掌通常具有浓厚的草本或木质叶绿素茎。仙人掌可以与其他多肉植物区分开来，它们的存在是：油菜籽，带有毛状体的小垫子状结构（植物毛），以及几乎所有物种中的刺或刺毛（硬毛）。槟榔是经过修饰的分支，可以从中生长出花朵，更多的分支和叶子（如果有）。
In most species, leaves are absent, greatly reduced, or modified as spines, minimizing the amount of surface area from which water can be lost, and the stem has taken over the photosynthetic functions of the plant. Only the tropical genera Pereskia and Pereskopsis, both vines, have conventional-looking functional leaves, while the leaves of the Andean Maihuenia are rounded, not flattened. The root systems are generally thin, fibrous, and shallow, ranging widely to absorb superficial moisture.
Cacti vary greatly in size and general appearance, from buttonlike peyote (Lophophora) and low clumps of prickly pear (Opuntia) and hedgehog cactus (Echinocereus) to the upright columns of barrel cacti (Ferocactus and Echinocactus) and the imposing saguaro (Carnegiea gigantea). Most cacti grow in the ground, but several tropical species—including leaf cactus (Epiphyllum), Rhipsalis, and Schlumbergera—are epiphytes, growing on other plants; others live on hard substrates such as rocks, while yet others climb far up trees. Epiphytic species tend to have thin, almost leaflike flattened stems. The appearance of the plant varies also according to whether the stem surface is smooth or ornamented with protruding tubercles, ridges, or grooves.
The primary method of reproduction is by seeds. Flowers, often large and colourful, are usually solitary. All genera have a floral tube, often with many petal-like structures, and other less colourful and almost leaflike structures; the tube grows above a one-chambered ovary. A style topped by many pollen-receptive stigmas also arises from the top of the ovary. The fruit is usually a berry and contains many seeds. Soon after pollination, which may be effected by wind, birds, insects, or bats, the entire floral tube detaches from the top of the ovary to leave a prominent scar.
Several cacti develop plantlets at ground level that, as offsets, reproduce the species vegetatively. Many others can reproduce by fragmentation, whereby segments broken from the main plant will readily root to form clonal individuals. Tissues of cacti are broadly compatible so that terminal portions of one species may be grafted on top of another.
The internal structure of cacti stems conforms to the pattern of broad-leaved angiosperms; a cambium layer of dividing cells, located between the woody inner tissues and those near the outside of the stem, is present. The bulk of the stem, however, consists of thin-walled storage cells that contain mucilaginous substances that prevent the loss of moisture. The stem of cacti is the main food-manufacturing and food-storage organ for most species.
Uses
Cacti are widely cultivated as ornamentals. In addition, various species, notably prickly pears and chollas (Opuntia and Cylindopuntia, respectively), are cultivated as food. In Central and South America, species of Opuntia, Cereus, and others are used as living fences, and wood from columnar cacti is used as fuel in some desert regions. In times of drought, the spines are removed from cacti such as mandacaru (Cereus jamacaru) to use as fodder for livestock. Peyote, from Lophophora williamsii, has been used ceremonially since pre-Columbian times for its hallucinogenic properties, and many cactus species are of local importance in traditional medicine.
