It's a slow-growth cactus, with a "cone" shaped type of growing. Of green-gray, being able to reach up to 30cm of height (which sometimes don't occur due to its easily detachable segments). According to the variety, each segment can have few (around 5) areolas or a lot (nearly 40). The trunk diameter is about 5cm and each segment can be of 10cm height.
Pretty easy plant to grow, due it's amazing cold and heat tolerance. This capacity allows it to grow in the nature in hot temperatures during summer and cold during winter (it can survive in -9°C). In nursery the soil in wich it is planted must allow excess water to be easily drained. During the hot seasons the watering should be in moderation (always waiting for the soil to be completely dry between each watering) and avoided during winter (or very little). It can be reproduced through seeds or, most common, from cuttings.
They pop mostly during spring. Quite small, of white or yellow color, that contrasts pretty nice with the grayish skin of the plant. It is said (haven't yet experienced so) that for the flowers to bloom it is needed that the plant does not receive water during winter. The specimen I own did have some watering but I live in a zone where winters aren't that cold and we sometime experience temperatures of around (or superior) 30°C.