Echinopsis is a genus of cacti indigenous to South America. The echinopsis genus, or group of species, contains 128 species of cacti. They range from large, tree-like varieties to small, hybrid varieties that are popular with cacti collectors.
The hedgehog cactus, Echinocereus triglochidiatus, is a common echinopsis species, and its pink to red cup-shaped flowers lead some to call it the claret cup cactus. The plant is short and barrel-like in shape, and it produces multiple cylindrical, clumped stems that reach up to 1 foot (30 cm) in height and up to 2.5 inches (6 cm) in diameter. The stems are produced in clumps to reduce the amount of exposed surface area, which minimizes the amount of heat lost during colder temperatures. This allows the hedgehog cactus to survive in slightly cooler temperatures and at higher altitudes than some other cacti. The hedgehog cactus has straight or slightly curved central spines up to 2 inches (5 cm) long and smaller radial spines that protrude from below the central spines at a sharp angle.
The sea urchin cactus, Coryphantha echinus, is a Texas native of the echinopsis genus that also is known as the rhinoceros cactus and the prickly beehive cactus. The plant is so popular with cacti collectors that it is under threat in the wild, where over-collecting wild specimens has seriously depleted the numbers of wild sea urchin cacti. The sea urchin cactus also is threatened by habitat loss, farming methods and the use of herbicides. Primarily a singular globe, the sea urchin cactus may clump or branch, especially in the wild at advanced maturity.
Flowers of the sea urchin cactus are fully expanded at midday if there is full sunlight but wilt after just one to two hours. The plant blooms from April through August. Central spines are not present until the sea urchin cactus reaches maturity. When central spines develop, they are around 1 inch (2.5 cm) long. Radial spines are present from immaturity and almost completely obscure the stems of the plant.
The cordon cactus, Echinopsis atacamensis, is an unbranched species native to Chile that grows to heights of 20 feet (6 m). This variety is able to tolerate some shade but prefers full sun. The average minimum temperature must not fall below 50 degrees Fahrenheit (10 degrees Celsius) in its growing area, because the cordon cactus is not tolerant of cold temperatures. The cordon cactus, like most cacti, does not need a great deal of water, and over-watering can cause root rot.