Etymology -From the Greek words echinos, meaning hedgehog and kaktos, meaning thistle.
The seemingly small genus of Echinocactus is widely accepted lately to include 6 species. Historically, the name Echinocactus has included many hundreds of species. This is a result of early cactus taxonomy in which a few names were used to cover large groups of cactus with an overall similarity with each other. In the case of Echinocactus any plants that were barrel shaped, ribbed, and not already included in Cereus or Melocactus found inclusion in the genus Echinocactus. The famous cactus taxonomists, Nathaniel Britton and Joseph Rose then moved most species into separate genera during the early 1900’s. There are some cactus enthusiasts who find themselves uncomfortable with the grouping of the remaining six species. They consider it largely a genus of convenience as there are differences between these six species that in other groups are used to define separate genera for otherwise similar species.
That being said, the remaining six species in Echinocactus do have several traits in common. Most significantly, they develop a dense, fuzzy wool at the apex which gives rise to the flowers in mature plants. This can be a wide, flat area covering almost the whole top of the plant in E. grusonii and E. platyacanthus or very limited and hardly noticeable as in E. texensis. Other similarities in this genus are an overall barrel shape and well-defined ribs. All species have robust spines and produce yellow or pink funnel shaped flowers. These later characteristics make Echinocactus appear very similar to the larger genus, Ferocactus aside from the wooly apex. Echinocactus fruits may be dry and wooly or fleshy and round.
While the many species that were previously included in Echinocactus ranged all over North and South America, the 6 remaining species are indigenous to the Southwestern United States and Mexico. In cultivation, the species E. grusonii - commonly referred to as the "Golden Barrel" - is easily one of the most popular of all cactus species grown. It is very easy to propagate from seed, grows fairly quickly, is tolerant of a range of treatment or mistreatment and has a striking appearance due to its golden-yellow spines. Ironically, it is nearly extinct in the wild and exists in only a very small area geographically. Conversely, the other species, are much more wide-spread, but are much less prevalent in cultivation. E. polycephalus is notoriously difficult to grow in cultivation due in part to its slow growth and affinity for high temps and low humidity.