Adenium obesum — The Desert Rose

Expert Agronome & Jardinerie indoor plant orchidaceae

Botany: Classification and Characteristics

Family and Genus

Adenium obesum belongs to the Apocynaceae family, which also includes plants such as oleander (Nerium oleander) and periwinkle (Vinca). The genus Adenium groups about ten species, all native to the arid regions of Africa and the Arabian Peninsula.

Morphology

• Caudex: swollen, fleshy trunk that stores water, characteristic of plants adapted to drought.
• Leaves: simple, alternate, obovate to elliptic, 5 to 15 cm long, dark green and slightly leathery.
• Flowers: funnel-shaped, 4 to 6 cm in diameter, grouped in terminal cymes. Variable colours: pink, red, white or bicoloured depending on the variety.
• Fruits: paired follicles containing seeds with silky hairs for wind dispersal.

The caudex can reach 1 metre in diameter in old specimens grown in open ground.

Drought Adaptations

• Waxy epidermis: reduces transpiration.
• Sunken stomata: limit water loss.
• CAM photosynthesis (Crassulacean Acid Metabolism): stomata open at night to capture CO₂, minimising daytime water loss.
• Water reserves in the caudex: allows survival through long periods without rain.

History and Discovery

Adenium obesum has been known for centuries by local populations of East and Southern Africa, as well as the Arabian Peninsula. The first botanical descriptions date back to the 18th century, when European explorers brought back specimens from their expeditions.

Origin of the Name

• Adenium: derived from "Aden", the old name of the Yemeni port city of Aden, where the plant is said to have been first described by European botanists.
• obesum: from the Latin "obesus" meaning "fat" or "fleshy", referring to its swollen caudex.

The plant is also called the Desert Rose because of its spectacular flowers, which evoke roses and contrast with its arid habitat. In some African cultures, the caudex was used to extract a violent poison used for hunting or fishing (the sap contains cardiotoxic glycosides similar to those of oleander).

Symbolism and Traditional Uses

• East Africa: a symbol of resilience and beauty in adversity.
• Yemen: a prized ornamental plant in traditional gardens.
• Traditional medicine: used with caution for its cardiotonic properties (high toxicity risk).

Care: Growing Indoors or Outdoors

Position and Light

Adenium obesum needs bright light to thrive and flower abundantly. Indoors, place it near a south- or west-facing window. An east or north exposure can work, but flowering will be less generous. Outdoors (warm climate), it tolerates full sun, but light shade during the hottest hours of summer is beneficial to avoid leaf burn.

Insufficient light causes etiolation and a lack of flowering.

Temperature

• Ideal: between 20°C and 30°C during the day.
• Minimum: 10°C (the plant goes dormant below 15°C).
• Maximum: tolerates up to 40°C if humidity is low.

In temperate climates, bring the plant indoors as soon as night temperatures drop below 12°C.

Watering

• Spring-summer (growing period): water generously when the substrate is dry to a depth of 2-3 cm. Let it dry out between waterings.
• Autumn-winter (dormancy): reduce watering greatly. One watering every 15-20 days is enough.

Excess water is the main cause of caudex and root rot. Use a very well-draining substrate.

Substrate and Repotting

Use a very well-draining mix to avoid standing water:

• 30% cactus or succulent potting mix.
• 30% perlite or pumice.
• 20% coarse sand (non-calcareous).
• 20% well-rotted compost (optional for actively growing plants).

Repot every 2-3 years in spring, when the roots come out of the pot. Choose a container slightly larger than the previous one, with drainage holes.

Fertilising

• Growing period (spring-summer): apply a cactus or succulent fertiliser, diluted by half, every 15 days.
• Avoid nitrogen-rich fertilisers, which encourage leaf growth at the expense of flowers.
• In autumn and winter, stop all fertilising.

Pruning and Shaping

Pruning is not compulsory, but it allows you to:

• Encourage branching and obtain a more compact shape.
• Remove dead or diseased branches.
• Control the size of the plant, especially for bonsai specimens.

Prune at the beginning of spring, before growth resumes. Use a clean, disinfected pruner to avoid infections. Wear gloves, as the sap is toxic and can irritate the skin.

Propagation: Seeds, Cuttings and Grafting

From Seeds

Propagation by seed is the most common method for obtaining new plants. Seeds germinate easily, but seedlings take several years to develop an impressive caudex.

• Harvest seeds from ripe fruits (opened follicles).
• Sow in a light mix (50% potting soil, 50% perlite) at a temperature of 22-25°C.
• Keep the substrate moist (not soaked) until germination, which occurs within 7-15 days.
• Transplant the seedlings when they reach 5 cm in height.

Plants grown from seed can show variations in flower colour and caudex shape.

From Cuttings

Cuttings reproduce a variety faithfully and produce a more mature plant faster than seeds.

• Take a 10-15 cm cutting from a healthy stem, using a clean knife.
• Let the cutting dry in the open air for 2-3 days to allow callusing.
• Plant the cutting in a draining mix (perlite or sand) and keep it slightly moist.
• Rooting usually occurs within 3-6 weeks.

Cuttings are prone to rot. Avoid excess water and use a natural fungicide (cinnamon powder) to prevent infections.

By Grafting

Grafting is used to propagate rare varieties or to combine several flower colours on one plant. The most common method is cleft or crown grafting.

• Use a vigorous rootstock (standard Adenium obesum) and a scion of the desired variety.
• Graft in spring, when the sap starts to flow.
• Maintain high humidity and a temperature of 25-30°C to encourage the union.

Common Diseases and Problems

Care-Related Problems

Caudex or Root Rot

Cause: excess water, poorly drained substrate or temperatures that are too low.

• Symptoms: soft, blackened caudex, yellowing and wilting leaves.
• Solutions: reduce watering, repot in a dry, draining substrate, treat with a fungicide (Bordeaux mixture).

Etiolation

Cause: lack of light.

• Symptoms: elongated, thin stems, small and widely spaced leaves.
• Solutions: move the plant to a brighter spot, prune the etiolated parts.

Pests

Mealybugs

Sucking insects covered with a waxy shell, attaching themselves to stems and leaves.

• Symptoms: white cottony masses, sticky leaves (honeydew), weakening of the plant.
• Solutions: remove mealybugs manually with a cotton bud soaked in alcohol, treat with black soap or a systemic insecticide.

Red Spider Mites

Microscopic mites that proliferate in dry, hot conditions.

• Symptoms: fine webbing on the leaves, yellowing and drying leaves.
• Solutions: increase ambient humidity, treat with a miticide or neem oil.

Aphids

Small green or black insects that feed on the sap of young shoots.

• Symptoms: deformed leaves, presence of honeydew, ants attracted by the honeydew.
• Solutions: spray with soapy water or a natural insecticide (nettle tea).

Fungus Gnats (Sciarid Flies)

Small black flies whose larvae feed on the roots.

• Symptoms: flies around the plant, damaged roots, slowed growth.
• Solutions: reduce watering, use yellow sticky traps, treat with Bacillus thuringiensis.

Physiological Problems

• Yellow leaves: excess water, nutrient deficiency or natural ageing.
• Leaf drop: water stress (lack or excess of water), sudden change in temperature or light.
• No flowering: lack of light, excess nitrogen in the fertiliser, unsuitable pruning.

Multifunctional Aspects

Ornamental Plant

Adenium obesum is mainly grown for its decorative appearance:

• Sculptural caudex: original, graphic shape, shown off in wide, shallow pots.
• Spectacular flowers: a palette of bright colours (pink, red, white, bicoloured) attracting pollinators.
• Evergreen foliage (in warm climates): brings greenery all year round.

Ideal for dry gardens, rockeries, conservatories or bright interiors.

Desert Bonsai

Thanks to its slow growth and imposing caudex, Adenium obesum is highly prized for creating desert bonsai.

• Techniques used: regular pruning, branch wiring, frequent repotting to limit growth.
• Result: miniaturisation of the plant while keeping a massive caudex and abundant flowers.

Adenium obesum bonsai need the same care as standard plants, with special attention to pruning and shaping.

Toxicity and Precautions

Adenium obesum contains cardiotoxic glycosides similar to those of oleander, present in all parts of the plant, but especially in the sap.

• Risks: heart problems, nausea, vomiting if ingested. Skin irritation on contact with the sap.
• Precautions: wear gloves when pruning or repotting. Keep the plant away from children and pets.

Varieties and Where to Find Them

Main Varieties

There are many varieties and cultivars of Adenium obesum, differing in flower colour, caudex shape or plant size.

Adenium obesum subsp. obesum

Type variety, the most widespread in cultivation.

• Flowers: pink with a darker throat.
• Caudex: thick and branched.
• Size: up to 2 metres in open ground.

Adenium obesum 'Black'

Rare variety with very dark, almost black red flowers.

• Flowers: dark red to black.
• Caudex: often finer than the type variety.
• Growth: slower.

Adenium obesum 'Double Color'

Cultivar with bicoloured flowers, often pink and white.

• Flowers: pink petals with a white throat or vice versa.
• Caudex: similar to the type variety.
• Popularity: highly prized for its decorative look.

Adenium obesum 'Variegatum'

Variegated variety with leaves edged in white or yellow.

• Leaves: green with cream or yellow margins.
• Flowers: pink, similar to the type variety.
• Sensitivity: more fragile, needs bright light to keep its variegation.

Adenium obesum 'Dwarf'

Dwarf variety, ideal for indoor growing or bonsai.

• Size: does not exceed 30-40 cm in height.
• Flowers: pink, proportionally large for the plant.
• Caudex: develops quickly, giving a very attractive miniature look.

Adenium obesum 'Thai Socotranum'

Hybrid between Adenium obesum and Adenium socotranum, originating from the island of Socotra.

• Flowers: pink with a red throat.
• Caudex: very thick and branched, reminiscent of Adenium socotranum.
• Growth: slower than the type variety.

Where to Buy Adenium obesum?

Adenium obesum is available in many garden centres, nurseries specialising in succulents, or online.

• Garden centres and nurseries: favour establishments specialised in succulents to find rare varieties.
• Online: specialist sites (e.g. specialist succulent shops, Etsy for rare varieties).
• Plant markets: some markets offer plants at attractive prices.
• Seeds: available on sites such as Amazon, eBay or specialist shops.

Beware of offers that seem too good for rare varieties. Check the reviews and the seller's reputation.

Prices

• Standard plants: between €10 and €30 depending on size and variety.
• Rare varieties (e.g. 'Black', 'Variegatum'): between €30 and €100.
• Seeds: between €2 and €10 for a packet of 5 to 20 seeds.
• Bonsai: between €50 and €300 depending on age and size.