Tabernanthe iboga: Botanical Profile

The botanical literature on iboga is small, mostly old, mostly French, and routinely misquoted by the much larger literature about the drug. This page stays with the floras.

Name and publication

Tabernanthe iboga Baill., family Apocynaceae, order Gentianales. Chromosome number 2n = 22.

The protologue appeared in the Bulletin Mensuel de la Société Linnéenne de Paris, volume 1, page 783. The year is given as 1888 by two Kew databases and as 1889 by two others, including the International Plant Names Index. We have not resolved it, and we mention it because a discrepancy between Kew’s own products is a fair warning about how thin the underlying record is.

Several synonyms are folded into the accepted name, among them Tabernanthe mannii Stapf, which matters because the pharmaceutical literature of the 1930s describes its product as an extract of Tabernanthe manii. The count itself is one more place the databases disagree: the global backbone folds in six, Kew’s own list gives a different figure, and we have not reconciled them.

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The other species

The genus contains two accepted species. Tabernanthe elliptica grows in the Congos and north-eastern Angola, differs in leaf venation and fruit structure, and hybridises with T. iboga.

Structure and habitat

A shrub or small tree to four metres, repeatedly dichotomously branched, with white latex throughout and a trunk to ten centimetres in diameter. Bark pale to dark grey and smooth. The fruit is a berry of three to six and a half centimetres, yellow to red, with many seeds in white pulp. Seeds are seven to ten millimetres and deeply indented.

It grows in forest understorey, sometimes riverine or swamp forest, and in relatively wet savanna. Its seeds are dispersed by elephants feeding on the fruit, which is worth holding in mind when reading about the plant’s future.

Native range, from Kew: Gabon, Cameroon, the Central African Republic, Congo, the Democratic Republic of the Congo, and Angola with Cabinda.

Shrub or tree?

Both words are used, and the disagreement is real rather than careless.

The floras describe Tabernanthe iboga as a shrub or small tree reaching about four metres, with a trunk to ten centimetres across, repeatedly branching in twos. That is at the shrub end of the range by most definitions: no single dominant trunk, branching low, and a height a person can reach the top of.

In cultivation and in open ground it grows taller and reads more like a small tree, which is where much of the photography comes from. Most images labelled as the iboga tree are of cultivated plants, and most people who search for the tree are picturing something considerably larger than what grows on the forest floor in Gabon.

The practical consequence is a slow one. It reaches roughly sixty centimetres in three years and takes five to six years to reproduce, and harvesting the root bark generally means taking the whole plant out of the ground. A plant that looks like a shrub and grows like one cannot be cropped like a tree, which is the arithmetic underneath the conservation question.

Chemistry

Modern work using high-resolution mass spectrometry assigned thirty indole alkaloids to the root bark, and the verb matters. Seven had been reported for this plant before: ibogaine, iboxygaine, ibogaline, catharanthine, ibogamine, voacangine and coronaridine. The other twenty-three are tentative assignments, matched against databases of compounds reported in other species. The same analysis left a further forty-eight peaks as unidentified alkaloids, accounting for about a fifth of the total.

So the root bark carries something like seventy-eight alkaloid features, seven of which are securely identified. “Thirty alkaloids have been identified” is the sentence that circulates, and it is not what the paper says. The other alkaloids of iboga takes those seven individually, with what is known about each and how thin that is.

Distribution by plant part, from PROTA: root bark five to six per cent total alkaloids, roots one to two and a half, stem bark two, seed one, leaves under one.

The leaves are a genuine exception rather than simply a poorer source. Work published in 2018 found they produce isoplumeran-type alkaloids rather than the ibogan types of the roots and stems.

What has never been measured

No study has quantified how alkaloid content varies between individual plants, or between geographic origins, using botanically verified material.

Everything published as variation is variation between products, with provenance asserted by whoever sold them. That distinction is not pedantic: it is the difference between a plant that is inherently unpredictable and a supply chain that is. Nobody has established which.