This is a large genus of about 200 species of cacti. It is a fascinating collection, represented by all manner of extraordinary shapes. They vary from those that grow close to the ground to those that have tree-like proportions. Most have flattened segments that form the branches giving the plants a characteristic cactus shape, but others are more cylindrical or even spherical.
They are all covered with spines, which should be avoided since they can cause skin irritation. They also contain barbed spines (glochids), which are difficult to remove if they pierce the skin. Once the plants have matured they produce flowers that are cup- or funnel-shaped. Their colours vary from yellow through orange to red, depending on the species, and appear in spring or summer. The species vary in hardiness, some are fully hardy and others are tender, which must be grown inside in cooler areas. If grown outside they all need a warm position in full sun and should be planted in a very-free-draining soil that is not too rich. Avoid planting where children may come into contact with them.