Gymnocalycium horstii, Spider Cactus is a choice and desirable Gymnocalycium from southern Brazil. Its squat globular body is particularly attractive with spider-shaped pale spines contrasting with the large open areas of green shiny epidermis that give it a somewhat naked appearance. It generally starts to offset as it matures and in time will form a large characterful specimen. The pink flowers which are borne freely in the summer are an added bonus.

It is listed on the IUCN Red LIst as Endangered and is under threat in the wild from agriculture and poaching.