Black locust

Symbiosis and the mushrooms that keep black locust company

Black locust (Robinia pseudoacacia) is an introduced species in Europe. David Arora notes in «Mushrooms Demystified» that introduced trees rarely form broad mycorrhizal ties with native mushroom species. That's why you'll practically never find classic mycorrhizal mushrooms such as porcini, slippery jacks or chanterelles under black locust.

Instead, black locust wood is extremely dense and distinctive, which makes it attractive to certain groups of wood-decay fungi. In the «Key to the Fungi of Ukraine», M. Ya. Zerova lists these mostly as saprotrophs (which break down dead wood) and parasites:

1. Oyster mushrooms (Pleurotus): The most welcome find on black locust. The oyster mushroom (Pleurotus ostreatus) and the pale oyster often colonize dead or weakened black locust trunks in abundance in autumn and spring.

2. Chicken of the woods (Laetiporus sulphureus): This bright yellow parasitic mushroom, edible when young, often attacks old living black locusts, causing brown heart rot.

3. Honey fungus (Armillaria mellea): An aggressive parasite that can appear en masse on the roots and stumps of felled black locust stands.

For a forager, a black locust grove is most productive in late autumn or even in a mild winter, when velvet shanks (Flammulina velutipes) and oyster mushrooms flush en masse on its wood.