is controversial. They are closely related, as shown by molecular genetic and other research: Ancistrocactus Britton & Rose Echinomastus Britton & Rose Glandulicactus Backeb. Homalocephala Britton & Rose Species the following species are recognized in the genus Sclerocactus by Plants of the World Online: Many species of Sclerocactus are protected under the provisions of the Endangered Species Act and all species should be treated as imperiled. Cultivation and propagation Sclerocactus are easy to cultivate. They are generally a cold-adapted genus. They grow in very arid areas which are subjected to deep cold in spots where water flows irregularly or depressions where water can accumulate for short period of time. They are most often found growing along washes and arroyos where their seeds have been subjected to scarification due to water movement, but they oddly also tend to grow along ridges in spots where depressions have formed and can hold water for some period of time. They undergo most of their growth in spring and benefit from moderate fertilizer in cultivation. They prefer mineral-rich, sandy soils. They are tolerant of overwatering provided they are grown in small pots that drain and dry out quickly. They do best out of doors do well in full sun. They are not particularly attractive plants and their vicious hooked spines are a hazard, making them poor houseplants. Like Pediocactus, Sclerocactus "deflate" in late fall in preparation for winter and freezing; they push water out of the plant flesh, through the roots, and into the soil, dramatically decreasing in size. They require deep cold and dormancy to bloom well. Some species, such as S. parviflorus, produce large, showy flowers and put a short, but impressive floral display in early spring. Sclerocactus seeds are difficult to germinate as they contain inhibitors, and require cold stratification, prolonged soaking, or scarification of the seeds to trigger germination. Seeds of members of this genus can take up to three years to germinate in some cases if not scarified or subjected to repeated freeze-thaw cycles in the presence of water. The plants are easy to maintain in cultivation but difficult to start from seed. References External links Southwest Colorado Wildflowers Utah Rare Plant Guide Cacti of Mexico Cacti of the United States Flora of the California desert regions Flora of the Great Basin Natural history of the Mojave Desert North American desert flora Cactoideae genera