The soft, opposite leaves of Mestoklema tuberosum are succulent and three-sided from a notable keel. The young leaf has water cells upon its surface making it rough-textured. The sometimes mucronate leaf-tips may curve back.
Leaves become 15 mm long, less than 5 mm wide. Leaf tufts grow from the axils. The hard leaf-base remains when old leaves drop off.
The stalked flowers grow in branched, cyme-shaped inflorescences. There are five, unequal, fleshy sepals with membranous margins, sometimes purplish at their tips.
The oblong to oblanceolate, round-tipped petals growing in a single whorl are orange to coppery, spreading to a diameter of 10 mm. There are numerous, whitish stamens gathered in a central cone, the inner ones bearded. No staminodes are present. Separate nectar glands form a discontinuous ring in the flower base around the five stigmas.
The flowers open around noon. The plants become spiny from retained, old flower stalks. Flowering happens nearly all year round, less in winter, more in spring and after rain.
The fruit capsule is small, 3,5 mm in diameter. It is Drosanthemum-like with five locules and valves recurving when expanded. There are no closing bodies (Vlok and Schutte-Vlok, 2015; Smith, et al, 1998; Herre, 1971; iNaturalist; http://www.llifle.com).