Notocactus parodia militaris
(This plant comes in a 3.5 inch pot. You will receive a very similar plant to the one in the picture. It may or may not be blooming at the time of your purchase. The plant is shipped in its pot to prevent any damage to the roots).
From southern Brazil, this species is also known as Parodia ottonis. It is a solitary plant when young, offsetting when older, and has green globose stems. The flowers are yellow to (rarely) orange-red.
Water requirements: Drought-tolerant.
Average water needs: Water regularly; do not overwater
Sun exposure: Sun to partial shade, light shade
Bloom time: Mid Spring, late Spring/early Summer
Soil: Needs excellent drainage in pots.
Some of the information in this description has been found at desert-tropicals.com, llifle.com and cactus-art.biz