Fly agaric (Amanita muscaria) accumulates significant amounts of vanadium from the soil. A small molecule natural product containing vanadium(IV) can be isolated from infructescence of fly agaric. The paramagnetic metal ion (EPR spectroscopy) is coordinated by two tetradentate hydroxyiminodiacetate ligands.
The complex is remarkably stable, which allows its accumulation in the soil in concentrations of up to 200 ppm. Its biological function has yet to be fully elucidated.