Erect, much branched, woody shrub, 2-3 (5) m tall (almost small tree size), bearing a single main stem up to 0.2 m in diameter. Wood white, reddish in mature plants and when dry, hard and brittle. Bark grey longitudinally fissured; younger branches succulent, reddish green, terete, about 2.5 mm in diameter.

Leaves in opposite pairs, sessile, succulent, ascending, sickle-shaped, oblong club-shaped, 20-35mm, bluish to reddish green, evenly covered with translucent dots, The leaf pairs are fused at their bases and form a short, distinctive, succulent sleeve down the stem (for up to 4 mm). Leaves of younger plants (and when growing in the shade) up to 55 mm long. The leaves are obscurely triangular in cross section with a blunt keel toward the end; the end (apex) blunt (rounded), and bearing a reddish, small, hard point.

Flowers are arranged in a dense compound inflorescence somewhat pyramidal or rounded in outline with up to 27 flowers, 20-55 x 40-60 mm (Figures 1 & 3). Bracts are club-shaped, leaf-like and becoming deciduous when fruits ripen. Flowers are top-shaped in outline, the upper part dome-shaped, 6 x 5-7 mm. Sepals are triangular, 3 mm long, 2.5 mm broad at the base. Petals are white, linear 3 mm long and spreading when open. Stamens and staminodes in a dense cone (yellow centre). Capsule 5 x 4 mm, valve wings 1 mm long at widest point; once opened, unlike most other mesembs, it remains open. The seed is pear-shaped, minutely papillate, 0.75 mm. Flowering time: July-August.

Stoeberia arborea is a distinct species differing from other stoeberias in several diagnostic features. In habit, it is distinguished by its tall, erect growth larger than all other species, in fact, it is the tallest of all Mesembryanthemaceae. The leaf arrangement and fruiting capsules differ in other species. Its flowers are also the smallest in the genus. Stoeberia carpii differs by its long ascending large leaves and long branches bearing large white flowers (largest in the genus).