Green Gills and Fairy Rings

This week's blog was written by guest blogger Dusty Purcell.  Dusty is a Mycologist/Plant Pathologist who studied at the University of Florida.

This is the ‘Green Gill Mushroom’, Chlorophyllum molybdites.  If you live in Pinellas County during the summer months, I am almost 100% certain that you have seen this mushroom.

For several reasons, it is an excellent first mushroom to learn:

1.  It has a cool name. Chlorophyllum molybdites.  Sound it out phonetically.  No one will dare correct your pronunciation. Trust me.

2.  It is extremely conspicuous.  These large pale mushrooms, often in large groups, poke up through the grass on sunny lawns and golf courses.  You can spot them while driving down the road.

3.  It is very common.  They pop up en mass around town every year during the warm and wet months.

4.  It is highly distinctive.  As far as I know, this is the only gilled mushroom with green spores.  Mature mushrooms have green gills (hence the common name).

5.  It is poisonous, being responsible for the majority of reported mushroom poisonings in Florida. Eating them can cause severe intestinal distress including cramps, vomiting, and diarrhea severe enough to require hospitalization.

You’ll find green gills following rains during summer and fall.  They may be alone but are more often found in groups.  They often sprout from the ground arranged in a line, arc or circle.  These circular arrangements of mushrooms are called fairy rings, and they are not uncommon sights in large open grassy areas like those found in parks and golf courses.  ‘Why do they grow in a ring?’ you may ask.  Well, have you ever seen mold growing on a Petri dish or a slice of bread?  The mold colony grows out from its center as a round expanding colony.  The fungus that produces this mushroom grows through the soil of a lawn in the same way.  As it gets larger the old central part of the colony dies, leaving a ring of living fungal colony to produce mushrooms when the weather is right.  They won’t hurt your grass… in fact they help decay grass clippings and other organic material in the soil.  This frees up nutrients for your lawn to use.  If, however, you are concerned about little ones (e.g. children and dogs) who put things found on the ground in their mouths, you may want to remove them from your yard.  You can pick them, put them in a bag, and throw them away with the trash.  This won’t eliminate the fungus from your yard, more mushrooms will likely sprout from the fungus growing in the soil, but it will make the yard safe for grazing family members.

On the left is an immature Green Gill mushroom.  The cap has not yet expanded to expose the gills. On the right is a slightly older specimen. The cap has begun to open, revealing the gills.  Notice the ring of tissue that was left behind on the stem where the margin of the cap had been attached.

You can find a thorough technical description in a good field guide to mushrooms.  Here you will find a simple but workable description and some decent pictures.  A good specimen may be 6-10 inches tall with a cap about as big around when fully expanded.  A ring of tissue encircles the stalk somewhere in its upper third, and the cap has tan to brown patches or scales clinging to its upper surface.  The gills are densely arranged on the underside of the cap and are not attached to the stalk.  The gills are white at first, but turn gray-green as the spores are produced.  The cap, stalk and ring may be white in fresh young specimens but are usually pale tan and darken to a light brown as the mushroom ages.  The gills, too, may turn brown as the mushroom ages.

The caps of these mushrooms have been folded back so you can get a good look at the color of the gills.  The one on the left is younger and still has white gills.  The specimen on the right is mature; the gills have turned green as they are now covered with mature spores.  Notice also how the stem has darkened with age.

Young specimens, with their white gills, can easily be mistaken for mushrooms of the genera Lepiota and Macrolepiota.  Old mushrooms, with their brownish gills, may be confused with members of the genus Agaricus.  So, even this highly unique mushroom has look-alikes. However, mature fresh specimens, with their distinctive green gills, cannot be mistaken for any mushroom that I know of.  A spore print, as seen in the photo below, is also a reliable way to determine spore color and confidently identify this neat toadstool.

This spore print was made from a fresh mushroom that still had white gills.  They are easy to make.  Just cut the stalk off of the mushroom and place the cap on a sheet of paper with the gills facing down.  It may take a while…  The heavy spore deposit here was made by placing a damp paper towel on top of the cap, setting an inverted bowl on top of it, and putting it in the refrigerator overnight.  The bowl and moist paper towel keep the mushroom cap from drying out.  Mushroom hunters make spore prints to determine the spore color for proper identification using field guides.

References and further reading:


Fairy Ring fact sheet from the University of Florida

Common Florida Mushrooms by James Kimbrough