The Pedaliaceae family belongs to the order Lamiales and comprises approximately 70–90 species in around 13 genera. Best known to the wider world through Sesamum indicum — the sesame plant, one of humanity’s oldest cultivated oilseeds — the family extends far beyond this single economic crop to include a fascinating array of plants adapted to arid and semi-arid environments. Among these, the pachycaul genera Uncarina and Pterodiscus have earned a devoted following among succulent plant collectors for their swollen stems, ornamental flowers, and extraordinary sculptural form.
Botanical characteristics
Pedaliaceae are characterised by their mucilaginous herbage — a sticky, gel-like coating on leaves and stems that traps insects and potentially assists in seed dispersal as well as deterring herbivory. The flowers are zygomorphic (bilaterally symmetrical), tubular, and typically showy, often in shades of white, yellow, pink, or violet. The ovary is superior and develops into a dry fruit — often armed with hooks, spines, or wings — that facilitates dispersal by attaching to the fur or feathers of passing animals. This mechanism is particularly well developed in the genus Uncarina.
Distribution and ecology
The family has its greatest diversity in Africa and Madagascar, with additional species in South and Southeast Asia. Most members favour open, sunny, warm habitats with well-drained soils, ranging from tropical dry forests to semi-desert scrubland. The pachycaul genera are concentrated in the driest zones: Uncarina is endemic to Madagascar’s arid south and west, while Pterodiscus is distributed across southern and eastern Africa, from the Karoo to the East African rift zone. Sesame, by contrast, is now cultivated across all tropical and subtropical regions of the world.
Pachycaul genera of interest
For succulent enthusiasts, the Pedaliaceae offer two genera of outstanding horticultural interest. Uncarina, endemic to Madagascar, develops a stout, swollen caudex from which deciduous annual stems emerge each growing season, bearing large, ornamental flowers in yellow or pink. Pterodiscus, from Africa, similarly develops a partially subterranean caudex, producing spectacular tubular flowers in pink, violet, or yellow — disproportionately large and showy for the modest size of the plant.
Both genera share the family’s characteristic hooked fruits, which grip and cling to any passing surface with remarkable tenacity. In the wild, this mechanism disperses seeds via large mammals. In cultivation, these fruits can become a minor nuisance but are nonetheless fascinating objects of natural engineering.
Economic importance
Sesamum indicum is the family’s most important economic contribution: sesame seed is cultivated globally for its oil-rich seeds, which are used in cooking, confectionery, and the production of tahini and sesame oil. The crop is drought-tolerant and heat-adapted, reflecting the family’s general preference for warm, dry conditions. Sesamum radiatum, native to tropical Africa, is also cultivated locally as a leaf vegetable. Beyond sesame, the Pedaliaceae have minimal commercial importance, though the ornamental potential of Uncarina and Pterodiscus is increasingly recognised by specialist nurseries.
Explore the pachycaul genera of the Pedaliaceae presented on this site to discover these remarkable plants in depth.