It’s been asserted that Mitragyna Speciosa is botanically related to genera Corynanthe and Uncaria, but where is the proof?
Firstly, mitragyna, corynanthe, and uncaria have the same taxonomy until the genus level:
Secondly, Mitragynine, the most abundant alkaloid in kratom, and its analogues, including speciogynine, paynantheine, and speciociliatine are indole alkaloids of the Corynanthe-type (Takayama, 2004).
Also, mitragynine pseudoindoxyl and corynantheidine pseudoindoxyls behave remarkably similarly. They are both opioid analgesics with mu agonism and delta antagonism, and neither recruit β-Arrestin-2 (Varadi, 2016). Such an astounding overlap in function is a sign that they are botanically related.
Mitragyna and Uncaria also have many overlapping alkaloids, including Angustine (Phillipson, 1974).
In his article “A revision of Mitragynaand Uncaria (Rubiaceae)“, Rivendale further draws similarities between mitragyna, corynanthe, and uncaria:
The Mitragyninae also form a rather isolated subtribe in the Cinchoneae but Corynanthe, Pausinystalia, and possibly Hymenodictyon, conventionally placed in the Cinchoneae, have the same characteristic insertion of the ovules and seeds. The results of a preliminary investigation tend to confirm the idea that these genera are more closely related to Mitragyna and Uncaria than to other genera of Cinchoneae; further investigation may show that they
belong to the Mitragyninae.
All of these indicate that mitragyna speciosa, corynanthe and uncaria are botanically related.