Ololiuqui is the Nahuatl name for the seeds of Turbina corymbosa, a white flowered morning glory of Mexico, and for their use in divination.
The practice is narrow and specific, and the colonial descriptions agree on it. A person with a question, ordinarily about a theft, a missing object, an absent relative or the cause of an illness, would consult a specialist, or take the seeds themselves; the seeds were ground and drunk; and the taker was placed in darkness and seclusion, sometimes with someone sitting by to listen, because the answer was expected to be spoken. This is divination in the strict sense, an instrument for getting information, not a ceremony of worship or a rite of passage.
The Spanish record is unusually good because it was hostile. The physician Francisco Hernandez described the plant and its effects in the sixteenth century, and the ecclesiastical authorities documented ololiuqui use extensively in the course of trying to extirpate it, producing manuals for identifying and punishing it. The Inquisition's interest generated the archive.
Related seeds of Ipomoea species, called tlitliltzin, were used in the same way, and both continued in use in Oaxaca and elsewhere into the twentieth century, where Zapotec and other communities were recorded still using them.