Mushrooms are masterpieces of natural engineering. The overnight appearance of the fruit body is a pneumatic process, with the inflation of millions of preformed cells extending the stem, pushing earth aside, and unfolding the cap. Once exposed, the gills of a meadow mushroom shed an astonishing 30,000 spores per second, delivering billions of allergenic particles into the air every day. A minority of spores alights and germinates on fertile ground and some species are capable of spawning the largest and longest-lived organisms on the planet.

Mushroom colonies burrow through soil and rotting wood. Some hook into the roots of forest trees and engage in mutually supportive symbioses; others are pathogens that decorate their food sources with hardened hooves and fleshy shelves. Mushrooms work with insects too, fed by and feeding leaf-cutter ants in the New World and termites in the Old World. Among the staggering diversity of mushroom-forming fungi we also find strange apparitions including gigantic puffballs, phallic eruptions with revolting aromas, and tiny “bird’s nests” whose spore-filled eggs are splashed out by raindrops.

Mushrooms have been around for tens of millions of years and their activities are indispensable for the operation of the biosphere. Through their relationships with plants and animals, mushrooms are essential for forest and grassland ecology, climate control and atmospheric chemistry, water purification, and the maintenance of biodiversity. This first point, about the ecological significance of mushrooms, is obvious, yet the 16,000 described species of mushroom-forming fungi are members of the most poorly understood kingdom of life.