Notocactus magnificus or Parodia magnifica
(This plant comes in a 3.5" 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).
Cultivation and propagation: Parodia magnifica is an easy to grow ornamental species suited for any well drained soil in half or full sun.
Growth rate: It is a relatively rapidly growing and easily flowering species that will make clumps given the best conditions.
Exposure: This plant need full sun but tolerate moderate shade, and a plant that has been growing in shade should be slowly hardened off before placing it in full sun as the plant will be severely scorched if moved too suddenly from shade into sun.
Watering: No water should ever be allowed to stand around the roots. Keep almost completely dry in winter. However this spurge will tolerate dryness and can even thrives in poor, dry soils, but do better when grown in nutrient-rich soils with regular watering.
Hardiness: Tender. This cactus cannot tolerate any frost and can be difficult to get it to look its best without a good amount of heat. It can be grown outdoors in frost-free climates.
Rot: Rot it is only a minor problem with cacti if the plants are watered and aired" correctly. If they are not
Some of the information in this description has been found at desert-tropicals.com, llifle.com and cactus-art.biz