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Echinocactus is a genus of cactus in the Cactaceae family. There is some discrepancy as to whether the genus contains six species or more, thereby making it confusing when classifying some of the cacti. These cacti naturally grow in low, open scrubland in parts southwestern United States and Mexico to parts of Brazil. Generally, they are round to cylindrical in shape, and distinctive with their prominent, heavily spined ribs and furry crowns. Gardeners raise many Echinocactus species as domestic plants, either in the garden or as houseplants.
Most Echinocactus cacti have diurnal flowers, meaning that they open in the daylight and close at night, and most are funnel or bell-shaped. Generally, the fruit is ovoid, white, and wooly. Growers usually propagate them by sowing the large, dark brown or black seeds in the spring when the soil is about 70°F (21°C). Most are hardy only to 20°F (-7°C) but some may a survive period of brief colder temperatures down to 10°F (-12°C). Young cacti rarely survive temperatures under 50°F (10°C).
The golden barrel, or E. grusonii, is one of the most popular with growers. As the name implies, it is a barrel-shaped cactus covered with golden areoles and spines and may grow to 24 inches (60 cm) tall and 32 inches (80 cm) wide. Some people call it the mother-in-law's cushion. The stem, or barrel part, often is bright green with 20 to 40 sharply angled ribs. The bright yellow flowers generally are 1.5 to 2.5 inches (4 to 6 cm) across and appear near the top center of the plant.
In contrast to the golden barrel, which often is a solitary cactus, the E. polycephalus is a clump-forming type of Echinocactus, with each stem being spherical and often elongated. Each gray-green stem may grow to be 28 inches (70 cm) high and 10 inches (25 cm) wide with 13 to 21 ribs. The light gray areoles have eight to 12 reddish-brown spines each. The yellow flowers average 2 inches (5 cm) across and sport pink outer tepals. It usually is native to southern Utah, northern Arizona, northern Mexico.
The mule crippler, or E. horizonthalonius, usually grows to be a 10 inch (25 cm) blue green globe with seven to 13 fat ribs. Each of the brown areoles usually has six to nine golden or light burnt sienna colored spines. The funnel-shaped, 2 inch (5 cm) wide flowers may be red or pink, depending on the variety, and usually have a darker shade near the flower base. This cactus generally is native in western Texas, Arizona, New Mexico, and northern Mexico.
Some botanists list the E. minuscule cacti, or red crown cacti, in the genus Rebutia, but many consider it an Echinocactus. These clump-forming cacti have spirally arranged tubercles, or nodules, instead of ribs. The areoles are on the tubercles and each one has 20 to 25 very short, white spines. When it blooms, this native of Argentina usually has 2 inch (5 cm) red flowers around the base and lower sides of the cactus.