Trichodiadema
Trichodiadema is a genus of small, shrubby South African mesembs (family Aizoaceae) whose short, plump leaves are tipped with a tiny crown of stiff bristles — the "diadem" that gives the genus its name. Several species thicken their roots into swollen, caudex-like tubers, and when these are lifted and displayed above the soil the plants take on the look of a miniature tree, earning them the affectionate common names desert rose (mesemb) and miniature desert rose. They are easy, floriferous succulents and a popular introduction to bonsai-style mesemb culture.
Description
Trichodiadema plants are low, much-branched subshrubs, typically only a few centimetres to a couple of hand-spans tall. The stems are slender and become woody with age, carrying pairs of small, cylindrical to club-shaped green leaves that are usually covered in tiny glistening bladder cells. The feature that unites the genus sits at the leaf tip: a rosette of short, radiating bristles (an areole-like tuft) that forms the characteristic little "crown".
Many species develop noticeably thickened, tuberous roots. Grown normally these stay hidden, but growers commonly raise the plant in its pot over several years and expose the swollen root as a natural caudex, which is what gives the group its bonsai appeal.
Flowers are typical mesemb daisies — many narrow, shining petals (petaloid staminodes) in shades of magenta, pink, purple or white, opening in sun and closing at night. They are large relative to the plant and are freely produced during the growing season.
Distribution
The genus is centred in South Africa, ranging into neighbouring parts of southern Africa such as Namibia. Most species grow in dry, open country, occurring in both summer- and winter-rainfall areas, rooting in gritty, well-drained soils among rocks and low scrub. As with all mesembs, the plants are adapted to bright light, sharp drainage and a distinct dry rest, and they resent sitting in cold wet soil.
Notable species
- Trichodiadema bulbosum — one of the most widely grown species; strongly tuberous-rooted and the classic choice for exposed-caudex "desert rose" bonsai, with bright magenta-pink flowers.
- Trichodiadema densum — dense little cushions of bristle-tipped leaves that look almost like a small cactus; showy purple-pink blooms.
- Trichodiadema mirabile — compact grower valued for its neat form and free flowering.
- Trichodiadema stellatum — spreading, mat-forming species with a woody, thickened base.
- Trichodiadema barbatum — a robust, bristly species from drier interior habitats.
Cultivation
Trichodiadema are among the more forgiving mesembs and make good beginner succulents. Grow them in a very free-draining, mostly mineral mix in bright light, ideally with some direct sun to keep the growth tight and the bristle-crowns well formed; too little light causes lax, etiolated stems and sparse flowering.
Water thoughtfully during the active growing season, letting the mix dry out between waterings, and reduce watering sharply during the plant's dormant rest. Most of the commonly grown species are warm-season (summer) growers that rest over winter, but the genus spans both summer- and winter-rainfall regions, so watch the individual plant and cut back whenever it stops actively growing. Keep them dry and airy in their rest period to prevent rot. They tolerate light frost when bone dry but are safest kept above freezing. See Watering and Repotting for general technique.
To develop the sought-after caudex, grow a tuberous species such as T. bulbosum for a few seasons, then repot with part of the swollen root raised above the soil surface each time until the "trunk" is well exposed.
Propagation
Trichodiadema are readily propagated. The most dependable routes are division of established clumps and seed sown on a fine mineral surface kept lightly moist and warm; seed-raised plants tend to build the best tuberous roots for bonsai training. Stem cuttings can also be taken in the growing season — cut a firm shoot, let the end callus for a week or two, then set it in a gritty mix — but they are more prone to rot than division or seed, so keep them barely moist until roots form.
Hobby and cultivar notes
In collections the genus is prized less for named cultivars than for the way individual plants can be trained. Growers select tuberous-rooted forms (especially T. bulbosum) and pot them progressively higher to reveal a gnarled, tree-like base, then let the crown of bristly leaves and bright flowers sit on top like foliage — a genuinely bonsai-like effect achieved without any wiring or heavy pruning. Because the plants branch, flower young and divide or root readily, they spread easily through succulent-society swaps and are a common gateway into the wider world of mesemb growing.
Common problems
- Rot — the main killer, almost always from overwatering, a slow mix, or water during dormancy; stems and the tuber soften and blacken.
- Etiolation — insufficient light produces stretched, floppy stems and poor flowering.
- Pests — mealybugs (including root mealybugs on the tuber) and the occasional spider mite; check the crown and roots at repotting. See Pests and diseases.
See also
- Aizoaceae — the mesemb family
- Mesemb — the broader group of "living stone" relatives and shrubby ice plants
- Soil and potting mix · Watering · Repotting · Propagation — cuttings · Propagation — seed