Echinocereus palmeri var. escobedoensis
Echinocereus palmeri var. escobedoensis is from Rio Florida, Durango, MX is a miniature mountain plant that can get a potato like root. These plants are very rare and fairly cold hardy. The largest plant ive ever seen was only 3 inches tall. We have had all three subspecies in the garden for a few years and they survived -17F this winter but im sure snow cover really helps them survive being so small of plants. The do get a sizeable flower that almost looks like a sombrero.
I do not guarantee these in a zone 4/5/6/7 because everyones growing conditions are different but this would be a good trial plant to grow in your cold outdoor garden. Try to plant outdoor 90 days before 1st hard freeze.