This species is a relatively recent plant in cultivation.  It has only been grown for ten or twelve years now, since being recognized by botanists in Presidio county, Texas.  The population is quite small, occurring only on nivaculite soils. E. viridiflorus v. nova is a small, clumping hedgehog cactus to 6 to 8 inches tall, with about the same diameter. (The potted plant in the picture is in a 6 inch diameter pot.)  In its juvenile form, it is covered with long white hairs, giving it a very different look from the mature form of white and purple colored straight spines.  The flowers are a clear yellow-green (thus the species name 'viridiflorus'--'yellow flowers').  This is a very floriferous species and here in Tucson is one of the first cacti to flower in spring, usually in March.