View photos of the medicinal plant Jatropha cardiophylla (Limberbush), profiled in Medicinal Plants of the American Southwest.

A passage from Medicinal Plants of the American Southwest:

All species of Limberbush are extremely astringent. The roots by weight contain approximately 5% tannic acid. This dominant phenol group (hydrolyzable tannin) is the reason why these plants are able to tan hides.