Gymnocalycium horstii is a globular cactus resembling a loaf of bread from a bakery. Plants have a squat appearance and spines that are curved back towards the body. Plants usually offset over time, creating interesting specimens. The body of this species is glossy and the flower is always white.
Gymnocalycium horstii is a very rare and threatened South American species and occurs only in the southern Brazilian province of Rio Grande do Sul.