The vernacular term Kratom refers to the Mitragyna speciosa var. Korthals tree and the products derived from its leaves, which concentrate the plant’s active principles.

The botanical classification of Mitragyna speciosa Kratom is as follows:

Division: Magnoliophyta
Class: Magnoliopsida
Order: Gentianales
Family: Rubiaceae
Genus: Mitragyna
Species: M. speciosa

The Mitragyna speciosa Kratom tree is in the Rubiaceae botanical family, a genus that includes many well know and useful psychoactive plants such as the Coffee tree (Coffea), the Yohimbe shrub, (Corynanthe yohimbe, former name of Pausinystalia yohimbe Pierre, Yohimbe), Cinchona ( which is a source of quinine) Psychotria viridis ( psychoactive plant which contains D.M.T. alkaloids) and Uncaria (of which the medical plant Uncaria tomentosa or Una de Gato / Cat’s Claw is well known).
Mitragyna speciosa Kratom is related to these plants of the Rubiaceae family, with which it shares some similar biochemistry and active alkaloids. Mitragyna speciosa Kratom’s alkaloid makeup and mode of action is complex, with chemical structures related both to opioids and tryptamines.
In the past, plants in the Mitragyna genus have also been sometimes been classified under the genera Nauclea, Sarcocephalus, Stephegyne and Uncaria.

The Mitragyna speciosa Kratom tree is indigenous to South East Asia, growing wild in Thailand, Malaysia, Indonesia and Papua New Guinea, yet also cultivated, mostly grown for leaf harvesting but also for its fine timber that can be carved and sculpted.

Mitragyna speciosa Kratom is a very widespread plant in Thailand, especially in the central and southern regions of the country, and only rarely in the north- situation which contributes to the difficulties of the Thai government to eradicate Kratom use. Feral Mitragyna speciosa Kratom trees are also common. Kratom is classified in the Mitragyna genus, which is found in tropical and sub-tropical regions of Asia and Africa, and also includes other plants that are used medicinally and for their wood.

Mitragyna speciosa Kratom and other Asian Mitragynas are most often found in rainforests, favouring wet, humus rich soil and a medium sun exposure in area protected from strong winds, while the African Mitragynas species (which are sometimes still classed in a separate genus, Hallea) are often found in swamps. The Kratom tree, Mitragyna speciosa, is an evergreen tree, which usually grows to a height of 3 to 15 meters and a branch width of 4 meters, yet in certain locations some 30 metre tall Mitragyna speciosa species have also been reported. Mitragyna speciosa has evergreen tree leaves, which are smooth, with a dark glossy green colour, and can grow over 18cm long and 10cm wide. Their shape is known ovate-acuminate, and opposite in its pattern of growth. Mitragyna speciosa is considered an evergreen plant rather than deciduous, and leaves are constantly being shed and replaced by new ones. Environmental conditions however, in a quasi-seasonal leaf shedding, with a more abundant leaf fall during the dry season, and a more abundant new leaf growth during the rainy season. When Mitragyna speciosa is grown outside of its natural tropical humid habitat, leaf fall usually occurs when the temperatures get colder, around 4° Celsius.

The Mitragyna genus was given its name by botanist Pieter Willem Korthals because the flower stigmas in the first species he examined resembled the shape of a bishop's mitre, reflected in the Kratom tree’s full denomination Mitragyna speciosa var. Korthals. Mitragyna Speciosa Kratom flowers are globular, yellow and grow in clusters of up to 120 florets each.

Ethnobotanical use of Mitragyna species other than Mitragyna speciosa Kratom, as medicine or for psychoactive effects, has been reported both in Asia and Africa but no detailed studies have been published yet.
West African species as Mitragyna inermis and M. stipulosa are known as traditional remedies against malaria, the former having also been shown by modern science to also help fight leukaemia. Another species, Mitragyna africanus, is traditionally used in Nigeria to treat mental illness, while M. ciliata (also known as M. ledermanni, M. stipulosa, Hallea ciliata, Hallea ledermanni or Hallea stipulosa) is traditionally used to treat inflammation, hypertension, headache, rheumatism, gonorrhoea and broncho-pulmonary diseases.