Definition
Mitragyna speciosa Korthals is a tropical evergreen tree of the madder family (Rubiaceae), genus Mitragyna. The species was first described by the Dutch botanist Pieter Willem Korthals in 1839, based on herbarium material collected during an expedition across Java and Sumatra. In Southeast Asia the plant is popularly known as kratom, ketum (Malaysia), biak-biak or thom (Thailand).
Taxonomy and classification
The systematic classification of the species:
- Kingdom: Plantae (plants)
- Division: Magnoliophyta (angiosperms)
- Class: Magnoliopsida (dicots)
- Order: Gentianales
- Family: Rubiaceae (madder family)
- Genus: Mitragyna
- Species: M. speciosa
The genus Mitragyna comprises approximately 7-10 species distributed across the tropics of Asia and Africa. Only M. speciosa is a significant source of mitragynine-type indole alkaloids; other species (such as M. parvifolia in India or M. inermis in Africa) have different phytochemical profiles.
As for subspecies, commercial literature sometimes cites a division by origin (e.g. "borneo", "bali", "malay"), but botanically these are ecotypes of the same species rather than formally described subspecies.
Morphology
Root and trunk
The tree forms a deep taproot with an extensive lateral system that allows it to survive dry periods. The trunk is straight and cylindrical, reaching a diameter of 50-90 cm in mature specimens. The bark is grey-brown, smooth in young trees and later fissured lengthwise.
Leaf
The leaves are simple, opposite, short-petioled, elliptical to ovate. A mature leaf measures between 14 and 20 cm long and 7-12 cm wide. The venation is pinnate, with a pronounced central vein showing through on the underside of the leaf. The colour of the central vein changes with the age of the leaf (from whitish-green through deep green to reddish) and forms the basis of the commercial classification of the raw material.
Flower
The inflorescences form spherical heads 2-4 cm in diameter, composed of dozens of small yellow to yellow-green five-part flowers. This structure is characteristic of the entire Rubiaceae family. The flowers are insect-pollinated, and the fruit is a small capsule with several seeds.
Growing conditions
The species requires a stable tropical climate:
- Mean annual temperature: 24-28 °C
- Annual rainfall: above 1500 mm, evenly distributed
- Air humidity: consistently above 70 %
- Soil: deep, permeable, slightly acidic (pH 5.5-6.5), rich in humus
- Altitude: 0-800 m above sea level
The tree is sensitive to permanently waterlogged sites (root rot) and to frost, which in Europe practically rules out cultivation in open ground.
Cultivation versus wild occurrence
Within its natural range, Mitragyna speciosa grows both wild (in lowland forests along rivers) and in a semi-cultivated form on village plots. Commercial plantations exist mainly in Indonesia (especially in Borneo), where seedlings are propagated by seed or cuttings. A plantation begins to yield usable leaf mass after 2-3 years, reaches full productivity after 5-7 years and then bears for decades.
Frequently asked questions
Who first described the plant?
Pieter Willem Korthals, a Dutch botanist, in 1839 in the work Observationes de Naucleis Indicis. The species name speciosa means "striking" or "showy".
How many subspecies are distinguished?
No formal subspecies are taxonomically described. Commercial names such as "borneo" or "bali" denote regional ecotypes of the same species.
Can it be grown in Europe?
Not in open ground (frost). In the greenhouses of botanical gardens, yes, but flowering and leaf-mass production are generally not achieved.
Does it differ botanically from the coffee tree?
Both species belong to the Rubiaceae family, but to different genera and tribes. The coffee tree (Coffea) has a different inflorescence (axillary clusters) and a different alkaloid profile (caffeine vs. mitragynine).
References
- Korthals P. W. (1839). Observationes de Naucleis Indicis. Verhandelingen van het Bataviaasch Genootschap van Kunsten en Wetenschappen.
- Sukrong S. et al. (2007). Molecular analysis of the genus Mitragyna existing in Thailand based on rDNA ITS sequences and its application to identify a narcotic species: Mitragyna speciosa. Biological & Pharmaceutical Bulletin, 30(7), 1284-1288.
- Raffa R. B. (Ed.) (2014). Kratom and Other Mitragynines: The Chemistry and Pharmacology of Opioids from a Non-Opium Source. CRC Press.
