A writhing plant root used by the Kahn-ut-tu healers of the planet Neural to draw out the otherwise fatal venom of the mugato in a ritual that binds healer and patient.
The mahko root appears in the episode A Private Little War. On the planet Neural, Captain Kirk is bitten by a mugato, a horned white ape whose venom kills within hours and for which Starfleet medicine has no antidote.
McCoy takes him to the hill people, where Nona, wife of Kirk's old friend Tyree, is a Kahn-ut-tu, one of the women who know the secret of the root. She cuts her own palm, presses the moving root between her hand and the wound, and draws the poison out in a trance-like ceremony.
Kirk recovers completely. According to local belief the rite joins the two souls, so that the patient can refuse the healer nothing, and Nona later tries to use that hold to obtain phasers for her husband's tribe.