Didierea trollii Capuron & Rauh is a succulent tree or large shrub endemic to the spiny forests of south-western Madagascar, family Didieraceae. The second species of the genus Didierea alongside D. madagascariensis, it differs in its bushier habit and shorter spines. Named after German botanist Wilhelm Troll (1897–1978).
Classification and nomenclature
Order Caryophyllales, family Didieraceae, subfamily Didiereoideae. Described in 1961 by Capuron & Rauh; current consensus maintains it as a distinct species from D. madagascariensis.
Synonyms
Didierea madagascariensis subsp. trollii (Capuron & Rauh) Rauh; Didierea madagascariensis var. trollii (Capuron & Rauh) Rauh.
Morphological description
Habit and dimensions
A tree or large shrub reaching 3 to 8 metres. Bushier than D. madagascariensis: more profuse branching, stems erect at first then gracefully arching outwards at the tips — a posture perfectly illustrated by the Palmetum de Tenerife specimen.
Stems and spines
Cylindrical, fleshy stems armed with spines in clusters of 3–4 at each node. In D. trollii, spines are shorter and more densely arranged than in D. madagascariensis — the most reliable field identification character.
Leaves
Small (10–20 mm), sessile, obovate, deciduous in the dry season. Reappear at spine bases with the first rains, clothing the stems in a dense green layer.
Flowers and reproduction
Dioecious. Small yellowish-green to pale pink flowers in terminal inflorescences. Fruits are 3-valved capsules. Flowering coincides with new leaf emergence.
Ecology and distribution
Endemic to the south and south-western tip of Madagascar (Ampanihy, Bekily, Tsihombe), in the Malagasy spiny forest. Grows alongside Alluaudia, Decaryia, Pachypodium, euphorbias, and baobabs.
Distinguishing Didierea trollii from D. madagascariensis
- Habit: bushier with arching tips in D. trollii; columnar in D. madagascariensis
- Spines: shorter and denser in D. trollii
- Range: more restricted to extreme south
Cultivation
Challenging — for experienced collectors. Full sun, high heat, sharply draining substrate. Cold-sensitive (damage from −1°C): overwinter at 12–15°C minimum. Water moderately in growth; near-dry in winter.
Conservation
Classified Vulnerable (VU) — IUCN Red List. Threatened by slash-and-burn agriculture, charcoal, overgrazing. CITES Appendix II.
References
Capuron, R. & Rauh, W. (1961). Didierea trollii sp. nov. — Rauh, W. (1995). Succulent and Xerophytic Plants of Madagascar. — IUCN (2024).