#217: Scleroderma citrinum, The Pigskin Poison Puffball

Scleroderma citrinum is characterized by a thick warty outer layer that is yellow-brown.

Scleroderma citrinum is a common earthball that appears in a variety of habitats around the world. The mushroom is one of the most often collected Scleroderma species, so one of its common names (mostly used in Europe) is “The Common Earthball.” S. citrinum has a couple other common names: “The Pigskin Poison Puffball” and the less common “Golden Scleroderma.” Both of these names refer to the mushroom’s outer surface, which is yellow-brown and has a scaly texture reminiscent of a football (American style, often called a “pigskin”). The mushroom’s thick warty outer skin makes it stand out among other earthballs and its interior that quickly turns blackish easily separates it from the true puffballs.^1–3

Description

Scleroderma citrinum is a medium-sized mushroom that grows 2-10cm across and 2-6cm tall. It is roughly circular from above and usually oval-ish when sliced in half. The Pigskin Poison Puffball doesn’t have much of a stipe, just a short plug of tissue at the surface of the ground that usually attaches to numerous threads of mycelium.^1–3

The interior of the Pigskin Poison Puffball starts out white but quickly becomes purple-black.

The outer surface of the mushroom is dull yellow to yellow-brown, though it sometimes fades to tan as it ages. S. citrinum is distinctive thanks to the texture of its outer surface, which is broken into regularly spaced angular scales that are slightly darker than their surroundings. The outer surface is very tough (scleroderma translates to “hard skin”) and the scales are no exception, so the mushroom’s outside is very rough. When S. citrinum is ready to release its spores, the top of the exterior surface rips open irregularly to reveal the mass of mature spores inside.^1–3

When sliced in half, it is clear that the mushroom is an earthball. Although it starts out solid and white, the interior quickly turns purple-black from the center out. For most of its development, the mushroom’s interior is firm. That changes once the mushroom is ready to release its spores. The interior becomes brownish black and powdery, which allows them to be dispersed by raindrops.^1–3

The Pigskin Poison Puffball has a very thick outer layer, which easily separates it from similar species.

Ecology

The Pigskin Poison Puffball is common and widespread in North America and Europe.^1,3 It probably grows all across the globe – there are scattered reports on MushroomObserver and iNaturalist from every continent.^4,5 S. citrinum appears in the summer through fall.^1–3

S. citriunum, like the other members of the genus Sclerodrema, is a mycorrhizal fungus. It readily forms mycorrhizas with a wide variety of trees and appears under both hardwoods and conifers. You usually find this mushroom growing on the ground in various environments (including poor soil), but it regularly appears on wood – an oddity among mycorrhizal fungi.^1–3 When it fruits from wood, the wood is usually well-rotted and often moss-covered. Since the mushrooms fruit from wood, there must also be mycelium growing in the wood. What is the mycelium doing there? It must be extracting some resource, but it isn’t clear what that is. Is S. citrinum acting as both a decomposer and mycorrhizal fungus? Maybe it’s just extracting water or vital nutrients from the wood. Perhaps the fungus is attacking nematodes or bacteria. This is a fascinating question, but the answer will have to await further research.

The Pigskin Poison Puffball sometimes has a bolete growing out of it. Boletus parasiticus presumably attacks S. citrinum parasitically, although the precise interaction is not completely understood.^1–3

The bolete Boletus parasiticus is sometimes found parasitizing S. citrinum

Similar Species

There are many earthballs that closely resemble one another: brownish spheres with thick skins that develop irregular tears in their outer layers. Fortunately, none of these other earthballs have prominent regular scales on their surface, making S. citrinum easy to pick out.⁶

Because it grows on wood, you could also confuse it with the Pear-Shaped Puffball, Lycoperdon pyriforme, or similar puffballs. Compared to S. citrinum, these mushrooms have much thinner skin, have a spongier texture, form regular openings, and have interior flesh that is whitish to olive. Additionally, any scales on their surface easily brush off.

When it gets old, the Pigskin Poison Puffball’s surface tears open irregularly to reveal powdery blackish-brown spores.

Edibility

The Pigskin Poison Puffball is toxic and should not be eaten.^2,3 However, I have heard that some people pick this mushroom when it is still white on the inside and grate it onto salads to add some flavor. This is similar to how people cook with truffles. If you want to try this, be very careful and be aware of the risks. S. citrinum produces more toxins as it ages, so the older it gets the greater the chance that it will make you sick. In my opinion, consider this mushroom poisonous (since it is poisonous) and don’t eat it.

Taxonomy

Fungi in the genus Scleroderma are most closely related to boletes. They are classified in the order Boletales and their closest relatives are fungi in the genus Gyroporus (such as G. castaneus, the Chestnut Bolete, FFF#200).¹ Despite its oddities, S. citrinum is a very typical bolete.