(This plant comes in a 3.5-inch pot. All our plants are grown under the same conditions, although not all the plants are the same. You will receive a similar plant in size and shape to the ones in the pictures. Our plants are hand-picked and carefully selected to bring you the best quality possible. Please allow us up to 3 business days to process your order. If you wish to receive your order on a specific date, or have special instructions, please add a note at the checkout. The plant is shipped in its pot to prevent any damage to the roots.)

Mammillaria petterssonii is a small cactus with a globular, usually solitary, light green stem with woolly axils and large 3-angled tubercles. The stem grows up to 4.8 inches in diameter. The tubercles bear 6 to 7 long central spines surrounded by 10 (or more) fine radical spines. The central spines are up to 2cm long, orange-brown, become whitish with age, and have a dark tip. The radical spines are white and up to 1cm long. Flowers are pinkish-red to white, with reddish midveins, up to 2.5cm long, and have a diameter equal to the length. 

Some of the information in this description has been found at desert-tropicals.com, llifle.com and cactus-art.biz