Most members of the Cactus family we encounter in North America are succulent, perennial, and herbaceous. The Cactaceae is an entirely American family, but one that been introduced unintentionally to other parts of the world. The peculiar fleshy bodies and shallow roots of typical cacti enable them to take advantage of short, sudden rainfalls and then survive the frequently long interval until the next rainfall. The flowers are large, solitary, and stalkless or sunken. There are large numbers of perianth segments that grade from bracts to sepals to petals. The stamens are numerous and thigmotropic, i.e., they move when touched. The pistil is single, 2- to many-celled, and compound, often with a large number of stigmas. The ovary is inferior and the fruit is a berry. The plants are usually leafless, with succulent green prickly stems modified into cylindrical segments or flattened lobes that regenerate readily if detached. Most of the 1000 to 2000 species are native to arid tropical and sub-tropical regions of the Americas.
Guide to Identify Presented Species of the Cactus Family
STEMS ROUND, BALL-LIKE
Escobaria missouriensis Yellow Pincushion Cactus Stems usually spherical, up to 5 cm tall. Valleys, hills and dry grasslands.
Flowers pale yellow, about 2.5 cm long, with many pointed petals.
Spines white, flat to spreading, in many clusters of several spines each.
STEMS WITH FLAT OR ROUND SECTIONS
Opuntia polyacantha Plains Prickly-pear Cactus Stems 10-30 cm tall, composed of several flat, oval sections. Dry hills.
Flowers yellowish to reddish, about 5-7 cm wide, with many broad petals.
Spines in many groups of 5-11, straight, 1-5 cm long, slightly barbed or not.
Alphabetical listing with links to presented species of the Cactus family: