Family Cactaceae > Subfamily Cactoideae > Genus Melocactus.
The 30 to 40 species are mostly native to Central and South America.
They are slow growing but are commonly cultivated.

They begin as solitary, spherical, green stems with many ribs.
The areoles down the ribs have short white hairs and long stout spines.
Each areole can have up to 15 spines that can be up to 6 cm long.
The longer, central 1 to 4 spines are nearly vertical and the rest radiate outwards.

When mature the stem stops growing and develops a flowering head.
The distinctive cephalium continues to grow and occasionally reaches 1 m in length.
It consists of a dense collection of areoles with woolly hairs and bristles or spines.
The hairs are initially white and may remain so but usually become reddish.

The flowers that form on the cephalium can be randomly placed or in a ring.
The small tubular red or pink flowers are often hidden by the woolly hairs.
More obvious are the white, red or pink club-shaped berries which rise above the hairs.

Melocactus bahiensis.

The green stems are spherical or slightly depressed spheres up to 20 cm wide.
They have 10 to 12 green or pale green ribs each with 6 or 7 areoles.
The white, woolly hairs are inconspicuous but the reddish-brown spines are up to 3.5 cm long.
There are about 10 radial spines and 4 or so central ones.

The cephalium has white woolly hairs and reddish-brown bristles.
The ratios vary with some heads being mostly white and others all reddish-brown.
The pink flowers are up to 2.5 cm long and just over 1 cm wide.
The tube is short and hairy.

The red club-shaped fruit are up to 2.5 cm long.
The other flower parts may remain attached.
The 1 mm seeds are shiny and black.

Melocactus peruvianus.

The Turk’s Cap or Melon Cactus is a very variable species.
The spherical to shortly cylindric, dark green stems are up to 20 cm high.
There are up to 15 ribs with areoles having white woolly hairs.
The yellowish to dark brown spines are up to 6 cm long but are variable.
There can be up to 15 straight or curved radial spines and 0 to 4 central ones.

The cephalium is usually small but can be up to 15 cm high.
The areoles have white hairs and reddish-brown bristles.
The red to pink flowers are only 1.5 mm across with a 5 mm long tube.
The pear-shaped red fruit are under 2 cm long.