There’s a Fungus among Us

A few weeks ago, we got 4 inches (10 centimeters) of rain followed by temperatures in the mid-90s (around 35 °C). Perfect conditions for the growth of fungi. In a nearby school ball field next to a woodland, I spotted a small Giant Puffball (Calvatia gigantea) among many other kinds of mushrooms.

Puffballs get their name from the habit of the mature fruiting body, the mushroom, to release clouds of brown spores when it is struck or bursts. There are several genera, including Calvatia, Calbovista, and Lycoperdon, that are known as puffballs, all in the division Basidiomycota. They are all grouped polyphyleticly, meaning that they share similar physical characteristics rather than a common ancestor.

Unlike most mushrooms, puffballs don’t have an outer cap of spore-producing gills. Instead, its spores are inside a round fruiting body called a gasterothecium (gasteroid means “stomach-like”).

The Giant Puffball is a saprotroph that feeds on non-living organic matter. It is more often found in meadows, grasslands, and forest openings, rather than in deep woods. It is seen throughout the eastern United States and Canada as well as throughout temperate Europe.

The species name gigantea is an apt description. Giant Puffballs have been known to grow to 59 inches (150 centimeters) or more in diameter! Typically, they can be from 4 to 27 inches (10 to 70 centimeters). Immature specimens are bright white. When seen from a distance they have been mistaken for soccer balls, and even sheep!

A mature Giant Puffball can contain trillions of spores—a 24-inch (61-centimeter) specimen can have 7 trillion! Why evolve to have so many spores? That amount ensures that at least a few germinate and grow to maturity. Imagine if each spore reproduced successfully. If one spore produced 12-inch (30-centimeter) offspring that all reached maturity, the resulting puffballs lined up would reach much more than the distance from the earth to the sun and back! Fortunately, that is impossible.

As it matures, a Giant Puffball develops cracks through which spores are released by the wind or by being stepped on by an animal. Other types of puffballs develop a hole at the top. The wind will suck out the spores like smoke from a chimney or spores can be forced out when the puffball is hit by raindrops.

Puffball spores have been used medicinally. The Lakota peoples of western North America have used the clean, dry spores to pack wounds. The spores act like a coagulant to slow or stop bleeding and prevent infection. In the 1960s, researchers isolated clavacin from the Giant Puffball, one of the first substances developed from a mushroom to have anti-tumor properties.

The next time you see a sheep on the hillside, better look twice.