Euphorbia obesa can grow to 20 cm in height with a diameter of 9 cm. It is a single-stemmed, unbranched, firm-bodied plant. The stem is usually 8-angled and grooved, subglobose (almost spherical) in shape, elongating and becoming cylindric as it gets older. Younger plants have a rounded sea urchin-like shape. The rotund stem is mottled grey-green in colour with dull purple transverse bands. It has a tapering tap root. The leaves are very rudimentary and soon drop off.
Euphorbia obesa is dioecious, i.e. male and female flowers occur on different plants. All euphorbias have a complex floral arrangement that is termed a cyathium (a cup) and this is the unit of the inflorescence. A cyathium contains many highly reduced male flowers or a single female flower. InEuphorbia obesa, the cyathia appear in summer, from "circular flowering eyes", situated along the tops of the angles, near the growing tip, on the stem. They are produced on fork-branched peduncles (flower stalks), have minute bracts and are finely hairy. The cyathia are cup-shaped to 3 mm in diameter, expanding in the female. The fruit is a slightly 3-angled capsule , up to 7 mm in diameter that explosively releases small rounded 2mm diameter mottled grey seeds when mature. The peduncles do not persist, and fall off after the seed has been dispersed.
Euphorbia obesa is best grown as a pot plant in a sunny position such as a window sill or stoep (verandah) but can also be grown out of doors in the Karoo and other desert gardens where frost is not too severe. It does best in a gravely shale based soil, but is tolerant of a wide range of soil types. Good drainage is essential. Water sparingly during the summer months and keep dry in winter. It is a slow growing long lived plant and once established, it will be content in its position and with its soil for years. It can tolerate moderate shade, and a plant that has been growing in shade should be slowly hardened off before placing it in full sun as the plant will be severely scorched if moved too suddenly from shade into sun.
Euphorbia obesa is easily propagated from seed sown during spring or summer. Sow in a sandy to gravel-rich, well drained potting soil in a sunny warm position and in a standard seed tray. Cover seed with a thin layer of sand (1-2 mm) and keep moist. Germination occurs within 3 weeks. The seedlings have a slow to medium growth rate and can be planted out into individual bags as soon as they are large enough to handle. Flowering can be achieved within 5-8 years. Plants can be hand pollinated with a small paint brush. Rub pollen onto the brush and transfer to stigmas of female plants. Remember to cover the female plants with a stocking or a net to catch the seeds, otherwise the capsules will shoot them far and wide.