Etymology -Refers to the characteristic flower tube of the genus. akantha. From the Greek meaning a prickle or thorn and kalyx meaning calyx.
This genus, comprised of three species, has for some time been kept separate from the large "catch-all" genus Echinopsis. From what I can tell, this is primarily due to the fact that the flowers come out near the stem tips. The flowers themselves, however do resemble Echinopsis flowers in that they have spines and wool on the scales and are relatively large. Flowers range in color from red to orange to white to yellow. The plant bodies are globose up to 6 inches in diameter and ribbed with between 16 and 20 ribs that are partially separated into tubercles. Some may form small clumps, but they are usually single-stemmed plants. Spines are about an inch or less and number between 10 and 20 per areole -initially yellow-brown, but turning gray as they mature. Fruits are scaly green balls about a half inch and contain brown/black seeds.
In The New Cactus Lexicon, Acanthocalycium has been placed back into Echinopsis.