Cactus plants (Opuntiacea-Cactacea) come in a wide range of sizes, shapes and colours. These tough succulents are well-adapted to arid conditions and generally thrive with little maintenance. According to the Clemson Cooperative Extension, as many as 2,000 types of cacti grow around the world, with the majority indigenous to North and South America. Most cacti grow in desert regions, but a few grow in tropical settings. All cacti produce flowers, some of which are very showy and grow up to 8 inches in diameter.
Stem and Flower Structure
Cacti belong to a family of stem succulents, or plants that store water in their stems. Stems swell to absorb and hold water, then contract during times of drought. Stems can be columnar, barrellike, cylindrical, branched or padlike. Unlike many vascular plants, most cacti do not produce leaves. Rather, their flowers grow from an areole, or spine cushion. Areoles grow in symmetrical lines along the barrels or ribs of a plant's stem or at regularly spaced intervals on pad-shaped stems.
The saguaro (Carnegiea gigantea) is the tallest cactus and the most common columnar type. Its stem generally grows up to 40 feet tall but can reach heights to 75 feet. This long-lived cactus can survive for more than 200 years and does not even begin to flower until it's 55 years old and at least 8 feet tall. Saguaros also begin to develop branching arms at about 50 years of age. Their white, 3-inch-wide flowers grow from areoles on the ends of their main stem and branched arms in late spring, followed by red fruits.
The members of the cholla genus (Opuntia spp.) have long, branched stems and produce flowers from areoles at the tips of both stem and branches. The buckthorn cholla and staghorn cholla (O. acanthocarpa and O. versicolor) grow from 3 to 15 feet tall and have green to purple stems. They produce flowers in a range of colours. The chainfruit or jumping cholla (O. fulgida) grows to 8 feet tall. It blooms in summer with 1-inch-wide pink flowers, followed by long-lasting chains of green fruits. The Christmas cholla (O. leptocaulis) has 2-foot-long stems and produces small pale yellow flowers in late spring that only emerge in late afternoon. Christmas chollas produce bright red fruits that last through winter. The pencil cholla (O. arbuscula) has an up to 9-foot-tall stem and blooms with green-yellow to brown-red flowers in late spring.
Barrel and Pad
The fishhook barrel cactus (Ferocactus wislizeni) has a 2- to 4-foot-tall, barrel-shaped stem. It blooms in late summer. The fishhook barrel cactus usually produces orange flowers, thorugh colours may vary. It also produces long-lasting yellow fruits. The prickly pear cactus (Opuntia spp.) grows from 1 to 5 feet tall and has flattened, wide stems that grow in several connected segments. It blooms with yellow-to-orange flowers that only last for a single day. Prickly pear cacti produce edible, purple-red fruits.
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