Cassia

True cinnamon is the inner bark of Cinnamomum verum, from Sri Lanka, and it is thin, pale, brittle and mild. Cassia is the bark of Cinnamomum cassia and its relatives, from southern China and mainland Southeast Asia, and it is thick, dark red, hard and much stronger. In most of the world outside Britain and Mexico, what is sold as cinnamon is cassia, and has been for a long time.

Both appear in Exodus 30. The holy anointing oil is myrrh, cinnamon, calamus and cassia in specified weights, mixed with olive oil, and the text is emphatic that the compound is not to be reproduced for ordinary use. Cinnamon and cassia being listed separately is one of the better indications that the ancient world distinguished them, whatever the modern spice aisle does.

In Chinese medicine cassia is rou gui, the bark, and gui zhi, the twig, and they are treated as different drugs with different actions. Rou gui is a major warming agent of the classical materia medica.

There is a practical reason to care. Cassia is high in coumarin, which is hepatotoxic in quantity, and several European food safety agencies have set tolerable intake levels that a heavy cassia consumer can exceed. Ceylon cinnamon has almost none.

Chinese tradition puts a cassia tree on the moon, and beside it a man named Wu Gang who is condemned to cut it down. Every stroke he makes closes behind him, so the tree is never felled and the punishment never ends. The story is usually attached to the Mid-Autumn Festival, when the moon is looked at most deliberately, and it sits alongside Chang'e and the jade rabbit as one of the standard lunar figures.

The osmanthus, gui hua, complicates the picture, since the same character does duty for both trees and later versions of the myth clearly mean the sweet-scented osmanthus rather than the cassia of the bark trade. Osmanthus flowers in autumn, which fits the festival, and its scent is one of the definitive smells of the Chinese year.

Passing the imperial examination was described as plucking a sprig from the moon's cassia, which puts the tree in the middle of the Chinese status system for a thousand years.

None of that has much to do with the resin trade, and that is the point worth making. A plant's ritual and literary life and its commercial life are separate histories that happen to share a name, and reading a text about cassia as evidence about the spice route will usually mislead. The Herodotean account of cinnamon being gathered from the nests of giant birds is the extreme case.