#041: Mushroom Morphology: Puffballs

The puffball is probably the second most familiar mushroom morphology. Many people can remember finding one of these as a child and giving in to the uncontrollable desire to kick the ball-shaped mushroom.  Anyone who has tried this knows that your efforts are rewarded with a fabulous puff of spores.  This puff is not just for the amusement of small children but is actually a rather ingenious spore dispersal mechanism.  Puffballs are gasteroid fungi, meaning that spores develop inside the mushroom.  All gasteroid fungi have lost the ability to forcibly discharge their spores, so they have to come up with other ways to release their spores.  Puffballs achieve this by puffing their spores out of small openings.  When the spores are mature a small opening (or a few small openings) called an ostiole develops on the surface of the mushroom.  When a raindrop (or an animal’s/ someone’s foot) lands on the surface of the mushroom, the surface is pushed down, which forces the spores inside up through the ostiole and into the air.

Another unifying feature of the puffballs is that their exterior surface (peridium) has two layers: an exoperidium on the outside and an endoperidium on the inside.  At maturity, the exoperidium sloughs off to reveal the endoperidium and ostiole.  This separates puffballs from earth stars, which have a three-layered peridium, and from earth balls (a.k.a. false puffballs), which have a peridium that breaks up at maturity to reveal the entire spore mass.  The most obvious morphological variations among the puffballs are the size of the mushroom and the shape of the exoperidium.  Puffballs have a wide range of sizes, from the tiny (2 to 5cm) Lycoperdon pulcherrimum to the giant (up to 5ft, 50lbs) Calvatia gigantea.  The exoperidium can be thin and mostly smooth, as in Bovistella radicata, or consist of large, showy spines, as in Calvatia sculpta.  Other less obvious variations among the puffballs include the presence or absence of a sterile base and the presence or absence of a system of capillitium that help the spores move to the ostiole.

Some species of puffball have a well-developed stipe and are known as “stalked puffballs.”  The stalked puffballs all start developing underground and the spores mature before or at the same time that the stalk begins to form.  The stalk pushes the puffball up through the outer covering, leaving a volva at the base of the mushroom.  At this point, two exceptions are worth considering.  The first is the stalked puffball Battarrea stevenii and its relative Battarrea phalloides.  These two mushrooms have a peridium that tears to expose the gleba and their spores are dispersed by the wind.  Although they resemble true puffballs, they are actually highly-modified agarics!  The other is the stalked puffball genus Calostoma (see FFF#106 for an example).  These odd-looking stalked puffballs have a gelatinous outer covering that falls off to allow spore dispersal through an ostiole as in traditional puffballs.  The odd thing about these mushrooms is that they belong to the Sclerodermataceae, making it a part of the earth balls (a.k.a. false puffballs).  As far as I know, these are the only Sclerodermataceae that discharge spores through a regular pore.

None of the puffballs are poisonous and many can be eaten!  There are a lot of small puffballs that are not considered edible due to their size.  All of the stalked puffballs are woody and are considered inedible.  The most commonly eaten genera of puffballs are Lycoperdon* and Calvatia.  When picking small puffballs for the table, you have to make sure that you don’t mistake them for false puffballs or amanita buttons, both of which can be poisonous.  In the case of amanita buttons, these can be deadly poisonous.  Every time you pick a small puffball you should cut it in half.  The interior, fertile surface (known as the gleba) should be a solid white.  If it has any color you either have a potentially poisonous false puffball or a true puffball that is just too old to eat.  If it does have color you should make sure to identify it to species before eating any nearby puffballs.  The other thing you could find upon slicing open a puffball-like mushroom is the outline of a toadstool in the center.  If you find this, DO NOT EAT IT!  It is not a puffball but an amanita button and may be deadly poisonous (see FFF#050 for an example).  If you’ve found a giant puffball, you don’t have to worry as much.  Both amanita buttons and false puffballs are medium-sized at the largest (usually less than 7cm in diameter).  Therefore any giant puffball is most likely a true puffball.  Remember, if the mushroom’s gleba has any kind of color you should not eat it.  The other thing to be careful about when handling puffballs is breathing in too many spores.  If you do, the spores could clog your airways like any other fine particulates.  In severe cases, the spores could germinate and try to be parasitic.  However, puffball hyphae are bad at being parasites, so the condition is easily treatable.

All of the puffballs discussed above (except those in the genera Battarrea and Calostoma) are found in the phylum Basidiomycota, class Agaricomycetes, order Agaricales, and family Agaricaceae.  I don’t know whether or not these puffballs form a monophyletic group.  They are all in the same family, so if they are not monophyletic they are still all closely related.  The family Agaricaceae also includes gilled mushrooms like Agaricus bisporus, the classic grocery store mushroom (see FFF#002 for more).  All of the true puffballs are decomposers of organic matter.  The most commonly encountered puffballs are found decomposing mulch.  The giant puffballs are usually found growing in grass rather than on wood.  The genus Calostoma belongs to the phylum Basidiomycota, class Agaricomycetes, order Boletales, and family Sclerodermataceae.  This order also contains all of the boletes, which have a central stipe and pores on the fertile surface under the cap (see FFF#028 for more).  Unlike the true puffballs, all genera in the Sclerodermataceae are mycorrhizal.

This post does not contain enough information to accurately identify any mushroom.  Never eat any mushroom without using a field guide to identify it.  If you need a free, quality field guide, I recommend Michael Kuo’s MushroomExpert.com.

* As a side note, the genus name Lycoperdon literally means “Wolf Fart.”  If you inhale too many spores from a Lycoperdon, you will end up with the condition lycoperdonosis, which means “wolf fart disease.”

See Further:

http://botit.botany.wisc.edu/toms_fungi/nov2001.html

http://botit.botany.wisc.edu/toms_fungi/aug98.html

http://www.mushroomexpert.com/puffballs.html (note: Kuo uses a broader sense of the word “puffball” than I do)

http://blog.mycology.cornell.edu/2006/10/26/giant-puffballs-calvatia-gigantea/ (for more on collecting puffballs to eat)

http://www.mushroomexpert.com/taxonomy.html