Botanical Bonsai: Senna meridionalis

A rare pachycaul treasure from Madagascar, prized for its naturally gnarled timber and sensitive, pinnate foliage.

1. Origin & History of Name: The genus name Senna is derived from the Arabic sanā, referring to the medicinal properties of plants in this lineage. The specific epithet meridionalis is Latin for "southern," identifying its primary distribution in the southern regions of Madagascar. It was formally reclassified into the Senna genus (formerly Cassia) by botanists to reflect its distinct floral and pod morphology.
2. Morphology: This species is a pachycaul shrub, characterized by a thickened, succulent trunk with a textured, peeling epidermis that mimics the appearance of an ancient tree. It features paripinnate leaves—small, oval leaflets arranged in pairs—which exhibit nyctinasty, the rhythmic closing of foliage at night. Unlike most Senna species, meridionalis grows extremely slowly, developing a zig-zagging branch structure that naturally suggests a bonsai aesthetic without intervention.
3. Habitat & Origin: Senna meridionalis is a wild species endemic to the calcareous and sandy plains of Southern Madagascar. Due to habitat loss in its native range, it is considered a high-value species for ex-situ conservation. Our specimens are nursery-propagated via seed or legal cuttings to ensure no impact on wild populations, supporting sustainable horticultural practices.
4. Cultivation Profile:
   • Substrate: Requires a strictly well-draining mineral mix. Use a base of volcanic rock, coarse sand, and a small fraction of coco-peat (80:20 ratio) to prevent root asphyxiation during the Indian monsoon.
   • Light: Thrives in full sun to bright indirect light. In the Indian subcontinent, it benefits from maximum exposure to maintain its compact, "bonsai" habit; however, protect the pot from overheating in extreme 45°C+ summer peaks.
   • Water/Dormancy: Provide regular water during the summer growing season once the substrate is dry. It undergoes a deciduous dormancy in winter; reduce watering significantly when leaves yellow to avoid rot.
5. Scientific/Historical Anecdote: Senna meridionalis is a prime example of "island gigantism" in reverse—while many Madagascar plants grew large, this species evolved a specialized, stunted growth habit to survive the brutal, desiccating winds and nutrient-poor limestone soils of the southern spiny forests. It remains one of the few members of the Fabaceae (legume) family cultivated specifically for its caudiciform qualities rather than its flowers.