Small succulent plants with characteristic stems, divided into four very pronounced vertical ribs. Along these grow the spines, which can vary in color and size depending on the variety. The flowers are peculiar and spectacular: they have a five-pointed star shape, with petals joined together to form a unique structure, in shades ranging from yellow to red and violet, often with very lively and pronounced streaks. However, they have an unpleasant smell, which in the wild serves to attract pollinating insects.