Gibbaeum

Gibbaeum is a genus of dwarf leaf succulents in the Aizoaceae or mesemb family. The perennial plants form compact clumps or leafy mats up to 20 cm in height, growing from woody rootstocks, some from fleshy roots.

The thickly succulent leaves are spherical or triangular in unequal pairs, variably fused at the base. The fissures between the pairs are oblique, leaf variations notable among the species. Leaf colour is pale or dark green, blue green, grey, greyish white or somewhat red. The leaf surfaces are usually hairy to velvety, the hairs varying in length.

The specific name, Gibbaeum, is derived from the Latin word gibbus meaning a hump, referring to the leaf-shape.

The solitary flowers without bracts grow stalked at stem-tips. The flower diameter is up to 2 cm. The flowers have six to nine, unequal, fleshy sepals.

The petals grow in one to three whorls, spreading around the flower centres on sunny afternoons only. Petal colour is white, pink or shades of purple or mauve.

Some species have staminodes around the stamens, often bearded at the base. There are usually six nectary glands in each flower. The ovaries are often nearly conical, each topped by six to nine stigmas.

Flowering happens from late winter to early summer.

The fruits are Drosanthemum-like capsules comprising six to nine locules topped by triangular valves. The expanding keels are toothed in some species and bear broad wings. There are covering membranes but no closing bodies. Many seeds are produced per locule. They are narrowly egg-shaped with smooth surfaces.

There are about 21 Gibbaeum species, mostly endemic to the Western Cape with slight representation of some species in the Northern Cape and a generic concentration in the Little Karoo. Some also grow south of the coastal mountains in the Overberg and near Riversdale. Many species are range restricted and most are adapted to arid conditions, growing in quartz gravel or on shale ridges.

The genus is similar to Argyroderma that is associated with the Knersvlakte.

Illegal plant collection plays a negative role in the safety of some species populations in nature. Tortoises and certain birds eat some Gibbaeum leaves. Some of the species are sensitive to the impact of ostriches and gemsbok introduced into their distribution ranges. Some species are commonly called ostrich water as they are eaten by ostriches. The plants may survive longer than 20 years in habitat.

The plant in picture is Gibbaeum dispar seen near Vanwyksdorp (Leistner, (Ed.), 2000; Vlok and Schutte-Vlok, 2015; http://pza.sanbi.org).