Euphorbia obesa aka Baseball Plant

Euphorbia obesa is a small, slow-growing succulent that forms a single ball- or short-barrel-shaped stem, typically reaching about 20 cm tall and 9 cm in diameter in mature SANBI specimens, with cultivated plants often falling in the 6-15 cm range described on Wikipedia. The stem is divided into eight prominent ribs and stays unbranched throughout the plant's life, so size changes happen gradually as the body fattens rather than by spreading or sending up new shoots.

In summer the apex of the stem produces tiny cyathia — Euphorbia's characteristic compound flower heads — only about 3 mm across, with no showy petals. Plants are dioecious, so male and female cyathia occur on separate individuals; you need both sexes flowering at the same time to set seed. Fertilized females develop small three-angled capsules up to 7 mm wide that explosively eject 2 mm seeds when ripe.

Wikipedia recognizes two subspecies of Euphorbia obesa — subsp. obesa and subsp. symmetrica — which differ in mature shape and the part of South Africa they come from. In horticulture these are sometimes sold simply as "baseball plant," but the more elongated form versus the squatter, more symmetrical ball generally distinguishes them.

E. obesa is well suited to outdoor cultivation only in dry, frost-free climates that mimic its Great Karoo habitat. SANBI recommends a sunny position in gravelly, well-drained soil, with sparing summer watering and a completely dry winter rest. Outside arid Mediterranean or warm-desert climates it is best grown in a pot that can be moved under cover for winter.

Propagation is from seed sown in spring or summer; SANBI reports germination within about three weeks. Because the species is dioecious and pods only produce two to three seeds, viable seed can be hard to source. Cuttings are not a practical route for this single-stemmed plant — it does not branch, so there is nothing to detach without destroying the specimen.

Slow growth is normal, not a sign of trouble. Wikipedia explicitly describes E. obesa as slow-growing, and that trait — together with sparse seed production — is one of the main reasons wild populations are vulnerable to over-collection. Expect a young plant to add only a few millimeters of diameter per year under good conditions.

Euphorbia obesa is dioecious, with male and female cyathia on separate plants, and is pollinated by small insects attracted to nectar glands within the cyathium structure rather than to petals. To set viable seed in cultivation you need a male and female plant flowering simultaneously, plus pollinator access (or hand-pollination).

When repotting, work in gravelly, fast-draining soil similar to its native Karoo substrate and handle with gloves and eye protection: any nick to the stem releases the plant's caustic milky latex, which causes painful skin irritation and serious eye injury on contact.

Pruning is generally not applicable — E. obesa is a single-stemmed, unbranched plant that grows as one tight ball, so there is nothing to shape. If a cut is unavoidable, wear gloves and eye protection because the milky sap is caustic to skin and especially damaging to eyes.

Dust the ribbed surface gently with a soft dry brush. Avoid wet wiping, which can leave the body damp around the ribs, and never cut or scrape the surface — the exposed milky latex is a strong skin and eye irritant.