Rainy weather can cause mushrooms to sprout in lawns and mulch. “That’s fine,” said Sharon Yiesla, plant knowledge specialist at The Morton Arboretum in Lisle. “What’s not fine is when you see mushrooms sprouting on trees.”

When a mushroom is growing on the trunk or roots of a living tree, or in the soil right around a tree, it indicates that there is a fungus growing in the tree’s wood. Decay-causing fungi can weaken the tree’s wood and make it structurally unsound.

“The mushroom is an alert, telling you to have an expert arborist come out and inspect the tree,” she said. “A trained, certified arborist can judge whether there is any cause for concern.”

Mushrooms are the short-lived fruiting bodies of fungi. Their function is to distribute microscopic spores that are carried away by win

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