Hydnocarpus is a genus of medium to large trees in the family Achariaceae, order Malpighiales, comprising approximately 37 species. The genus was formerly placed in the now-defunct family Flacourtiaceae, and a number of its species were previously assigned to the segregate genus Taraktogenos.
Trees in this genus bear simple, alternate leaves and produce small, dioecious flowers arranged in racemes. The fruits are woody capsules or berry-like structures with numerous oily seeds. Several species — most notably Hydnocarpus pentandrus (syn. H. wightianus) — yield chaulmoogra oil and hydnocarpus oil from their seeds. These oils are composed of unusual cyclopentene fatty acids, including hydnocarpic acid and chaulmoogric acid, which are not found in most plant oils.
Species are distributed across South and Southeast Asia, with records from India, Indochina, Indonesia, Malaysia, and the Philippines. They typically grow in tropical moist deciduous forests. At least one species, H. kurzii, is also cultivated in parts of Africa for its oil. A species of Hydnocarpus is noted as a host of the Peacock mite (Tuckerella filipina).
The genus is historically significant: chaulmoogra oil derived from Hydnocarpus seeds was the primary treatment for leprosy for centuries in Asian traditional medicine, and was adopted into Western medicine in the mid-19th century. The first effective injectable formulation was developed by chemist Alice Ball in 1916. The oil was eventually superseded by sulfone antibiotics in the 1940s.
Distribution
Species of Hydnocarpus are native to South and Southeast Asia, with records from India (especially the Western Ghats, Assam, and Tripura), Indochina, Indonesia, Malaysia, and the Philippines. Some species, such as H. pentandrus, are also cultivated in Sri Lanka, Nigeria, and Uganda.
Ecology
Species of Hydnocarpus are trees of tropical moist and moist deciduous forests in South and Southeast Asia. H. pentandrus grows along the Western Ghats of India in coastal and hilly forest zones, sometimes planted on roadsides in hilly areas. At least one Hydnocarpus species serves as host to the Peacock mite (Tuckerella filipina), a notable acarological record for the genus.
Cultural Uses
Seeds of several Hydnocarpus species yield chaulmoogra oil and hydnocarpus oil, long employed in Ayurvedic medicine, Chinese traditional medicine, and other Asian healing traditions, primarily for leprosy and a range of skin diseases. The oil was taken internally, applied topically, or later administered by injection. The tree is known by numerous vernacular names across India, including chaulmoogra (Hindi), marotti (Malayalam/Tamil), and tuvaraka (Sanskrit).
History
Chaulmoogra oil from Hydnocarpus seeds has been used in Ayurvedic and Chinese traditional medicine for the treatment of leprosy for centuries. It was introduced to Western medicine in the mid-19th century by Frederic J. Mouat. In 1904, Frederick Belding Power of the Wellcome Chemical Research Laboratories isolated hydnocarpic acid as the key active compound. In 1916, chemist Alice Ball developed the first water-soluble, injectable form of the oil (the ethyl ester "Ball method"); her work was initially published without credit by Arthur L. Dean. The commercial preparation sodium hydnocarpate (Alepol), manufactured by Burroughs Wellcome (now GlaxoSmithKline), was released in 1927 and represented the state of the art until sulfone drugs rendered it obsolete in the 1940s.
Taxonomy Notes
Hydnocarpus was formerly classified in Flacourtiaceae, a broadly defined and now-dismantled family. Molecular phylogenetic studies led to its transfer to Achariaceae within the order Malpighiales. Several species previously placed in the segregate genus Taraktogenos have been transferred to Hydnocarpus; H. pentandrus itself was long known as H. wightianus or Hydnocarpus wightiana in older literature.
