Adenium
Adenium is a small genus of caudiciform, succulent shrubs and small trees in the dogbane family Apocynaceae, native to the arid regions of sub-Saharan Africa and the Arabian Peninsula. Grown worldwide for their swollen, sculptural trunks and lavish trumpet-shaped flowers, they are known collectively as the desert rose and are among the most popular flowering succulents in cultivation.
Members of Adenium store water in a fat, woody base called a caudex, which — together with their showy pink, red and white blooms — makes them prized both as flowering pot plants and as subjects for bonsai-style training. Like many Apocynaceae, they carry a milky, toxic sap, so they are best kept away from curious pets and children.
Description
The defining feature of the genus is the caudex: a thickened, water-storing trunk and rootstock that can swell into a rounded, bottle-like or gnarled shape with age. Above this rises a branched framework of thick, tapering stems tipped with clusters of glossy, deep-green leaves. Most species are deciduous or semi-deciduous, dropping their foliage during the dry season or in cool winters and resting until warmth returns.
The flowers are the other great draw — broad, five-lobed trumpets, typically 4–6 cm across, in shades of pink, rose, crimson and white, often with a paler throat and darker margins. Modern hybrids extend the range to doubles, near-blacks and multi-toned picotees. All parts of the plant exude a milky latex when cut, which is irritating and toxic if ingested.
Distribution and habitat
Adenium ranges across the drylands of eastern and southern Africa — from the Sahel and the Horn of Africa down to South Africa — and across the Red Sea into Arabia, reaching Yemen, Saudi Arabia and Oman. Plants grow in rocky, well-drained ground in savanna, thornscrub and desert, where the caudex helps them ride out long dry seasons and the deciduous habit conserves moisture.
The best-known and most widely grown species, Adenium obesum, is the source of most cultivated forms and the parent of the great majority of named hybrids.
Notable species
- Adenium obesum — the common desert rose; the most widely grown species and the backbone of hybrid breeding.
- Adenium arabicum — noted for a broad, squat, often multi-branched caudex; a favourite for fat-base specimens.
- Adenium swazicum — a smaller, more slender species from southern Africa with pink flowers, valued in hybridising.
- Adenium multiflorum — the southern African "impala lily", strongly deciduous and free-flowering in the dry season.
- Adenium somalense — a taller, tree-like species from the Horn of Africa with a tapering trunk.
- Adenium boehmianum — a stout species from Namibia and Angola.
Botanists have at times treated several of these as subspecies or varieties of a broadly defined A. obesum; hobbyists generally keep the traditional species names.
Cultivation
Adenium is a warmth-loving, sun-loving genus and one of the more rewarding flowering succulents for a bright windowsill or greenhouse. Grow it in full sun to very bright light — the more light, the fatter the caudex and the better the flowering. Use a gritty, very free-draining mix; a mostly mineral blend suits the swollen roots best and guards against rot.
Water generously through the warm growing season, letting the mix dry out between drinks, then taper off sharply as temperatures fall. In winter, or during the plant's natural dormancy, keep it warm and nearly dry — Adenium resents cold, wet roots and is not frost-hardy, so keep it comfortably above freezing (roughly USDA zones 11–12, or indoors in cooler climates). Feed with a dilute balanced fertiliser during active growth to fuel flowering. See Watering and Repotting for general technique.
Many growers lift the plant slightly at each repotting to expose more of the caudex and roots, gradually developing the characteristic fat, sculptural base.
Hobby and cultivar notes
The desert rose has been bred intensively, especially in Thailand and Taiwan, producing an enormous range of hybrids selected for flower colour, doubled or ruffled petals, and heavy, ornamental caudices. Choice flowering hybrids and variegated forms are usually propagated by grafting onto a vigorous seedling rootstock, since cuttings and grafts flower true to the parent while seedlings vary. Seed-grown plants, on the other hand, develop the most naturally swollen, well-rooted caudex and are preferred where the fat base is the goal.
Because grafted and cutting-grown plants often lack the broad taproot-style caudex of a seedling, the two propagation routes suit different aims — showy blooms versus a fat trunk.
Propagation
Adenium is grown from seed, cuttings, and grafting. Fresh seed germinates quickly in warm, well-drained conditions and gives the best caudex development. Cuttings root readily in warmth but tend to form a narrower base. Grafting is the standard way to fix and multiply named hybrids and variegates. See the linked guides for full technique.
Common problems
- Rot — the commonest cause of loss, from cold, wet or poorly drained roots; the caudex softens and browns. Keep the plant warm and let the mix dry between waterings.
- No flowers — usually too little light; Adenium needs strong sun to bloom well.
- Pests — mealybugs, spider mites, scale and aphids can trouble stressed plants. See Pests and diseases.
Toxicity
Like many Apocynaceae, Adenium contains toxic compounds in its milky sap, and all parts should be considered poisonous if eaten. Wash hands after pruning, keep the sap out of eyes, and site plants away from pets and small children.
See also
- Adenium obesum — the common desert rose
- Apocynaceae — the dogbane family
- Grafting · Soil and potting mix · Watering · Repotting · Propagation — seed · Propagation — cuttings · Pests and diseases