Adenia
Adenia is a large genus of flowering plants in the passionflower family (Passifloraceae), native across the tropics and subtropics of Africa, Madagascar, the Arabian Peninsula and Asia. Many species are caudiciform and pachycaul succulents, grown mainly for their boldly swollen stems and water-storing trunks rather than their modest flowers; several of these have become sought-after "fat plant" collectibles that pair a dramatic caudex with slender, twining climbing shoots.
Description
Members of Adenia are enormously varied in form, but the cultivated species nearly all share the family trait of storing water in a swollen structure. In some this is a squat, above-ground caudex — a smooth, bottle- or turnip-shaped trunk that can be green, grey or coppery — while in others the swelling is a partly buried tuber. From the top of this water-store rise thin, often vining stems that scramble through surrounding vegetation, frequently carrying tendrils like their passionflower relatives.
The leaves are typically thin and deciduous, dropped during drought so the plant can rest on its stored reserves, and they range from simple to deeply lobed depending on the species. Flowers are generally small, greenish or yellowish and far less showy than a true passionflower; most species are dioecious, meaning male and female flowers occur on separate plants, so both are needed to set the small capsular fruit and seed. Many Adenia contain toxic compounds in their sap and tissues, and some are notably poisonous, so they are best kept away from pets and children and handled with clean hands.
Distribution
The genus is centred on continental Africa and Madagascar, with additional species reaching into the Arabian Peninsula and across to tropical and subtropical Asia. Most caudex-forming species come from seasonally dry woodland, thornscrub and rocky slopes, where a long dry season favours the water-storing habit and the deciduous, drought-avoiding foliage.
Notable species
- Adenia glauca — a popular beginner's species forming a smooth, grey-green domed caudex topped by climbing shoots with lobed leaves.
- Adenia spinosa — a large South African species that can build a massive, rounded trunk over many years, with spiny older growth.
- Adenia digitata — a tuberous African species with finely divided leaves; notably toxic.
- Adenia glomerata — grown for its coppery, often branching caudex and reddish stems.
- Adenia fruticosa — a shrubbier, thick-stemmed form from southern Africa.
- Adenia venenata — a green-trunked species whose name reflects the poisonous sap common in the genus.
Cultivation
Most Adenia are rewarding but slow, and — like other caudiciforms — far more likely to be killed by overwatering than by neglect. Grow them in a very free-draining, mostly mineral mix in a pot only a little larger than the caudex, and give plenty of warmth and bright light; the swollen trunk colours and firms up best in strong sun, while too little light produces weak, etiolated climbing growth.
Water regularly through the warm growing season once the mix has dried, then taper off sharply as the plant drops its leaves and enters winter dormancy. During the cool, dormant months keep them nearly dry and frost-free — a caudex left wet and cold will rot. Many growers raise the caudex progressively higher out of the soil at each repotting to show it off, though in habitat it often sits partly buried. Watch for the usual pests such as mealybugs and spider mites on the soft climbing growth, and remember that the sap can irritate or poison — wash your hands after pruning. General guidance in Watering applies.
Hobby and cultivar notes
Adenia are collected above all for the character of the caudex, and much of the interest lies in choosing species and individual plants with well-shaped, well-coloured trunks. Named cultivars are uncommon; instead growers prize seed-grown plants selected for form. Because most species are dioecious and seed requires both a male and a female plant, seed can be scarce and slow, which keeps choice specimens desirable among caudiciform enthusiasts.
Propagation
Seed is the primary and most satisfying method: sown fresh on a warm, mineral surface kept lightly humid, seedlings develop a natural, rounded caudex from the start — see Propagation — seed. Cuttings will sometimes root but typically grow into a thin-stemmed plant that is slow to build (or may never build) a good caudex, so cutting-grown material is generally less valued; see Propagation — cuttings for technique. As with all self-collected material, propagate only from cultivated plants, never wild ones.
See also
- Soil and potting mix · Watering · Repotting
- Propagation — seed · Propagation — cuttings
- Pests and diseases
- Caudex — the water-storing trunk that defines the group