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Identifying Agaricus in Colorado

By Ellen Jacobson, CMS Sociologist

It's time to unravel the mysteries of the great Genus Agaricus, a group of mushrooms that we all recognize, but frequently shy away from. The characteristics of the genus include free gills, chocolate brown spores, the presence of a veil (ring), medium to large size and a central stalk that separates easily from the cap. So far so good, but how do we tell the individual species apart?

For species identification, we need to rely on our sensitive noses and our discriminating color perception. Agaricus fortunately have quite distinctive odors. They may smell of almonds or anise, have a fungal odor or emit a very unpleasant chemical smell. It is important to aggressively stick your nose into the gills or the crushed flesh of a freshly squeezed mushroom to pick up the various odors.

The staining reaction that may occur when the stalk and/or cap is crushed can also be quite distinctive. There may be no color change at all, or the flesh may change to yellow, amber, red or reddish-brown in the stalk, the cap or both. It is best to check for odor and color changes when the mushroom is fresh as both the smell and the color can fade with time. Agaricus have prominent veils that are single, double, evanescent, pendant or sock-like. This genus is known to cause some allergic reactions in some people. If you have problems with store-bought Agaricus, then be very cautious when eating wild Agaricus. These are my rules for eating known and unknown Agaricus. There seem to be several in Colorado that are edible, but not well described. So, identification to species is not always possible:

1. Do not eat Agaricus that smells like a chemical--i.e. phenol, library paste, etc. If you are suspicious, but can detect no odor, begin to cook the sliced mushroom and then smell the vapors coming from the pan.
2. Do not eat Agaricus that stain yellow or amber at the base of the stalk when it is cut vertically.
3. Do not confuse the chocolate-spored Agaricus with the green-spored Chlorophyllum, the white-spored Lepiotas and Amanitas, or the Stropharia with attached gills.

Agaricus are very common in the city, especially on lawns and in cemeteries and parks where the grass is well watered. The most common Agaricus include the following, and June seems to be their favorite month:
1. Agaricus campestris: Found in grass. A short-stalked mushroom with an evanescent veil and bright pink gills when young. The odor is fungal. Does not stain. Kid-glove cap. Edible and delicious.
2. Agaricus bitorquis: Found in the hard-packed, bare dirt of bus stops and paths. Makes mushrumps (humps in the ground caused by mushrooms beneath). Very sturdy mushroom with a sock-like veil. Fungal odor may show reddish brown discoloration. Edible and the bugs like it, too.
3. Agaricus arvensis: Grows in grass and is a tall, stately, very large mushroom with a prominent double, cogwheel veil. It has a distinct, sweet odor and stains yellow. It is exceptionally delicious and is my favorite.
4. Agaricus xanthodermis: Grows in grass and, when young, has a cap the shape of a marshmallow--flat on top, round on the sides. The top center of the cap usually has a greyish brown center. The odor is UNPLEASANT, and the base of the stalk stains instantly yellow when cut. This is a poisonous mushroom. The medicinal smell will become more pronounced if the mushroom is cooked. It also tastes bad.
5. Agaricus "Ketring Park:" A large, fleshy, heavy, underground mushroom probably related to A. bitorquis that grows on the edges of dead grass patches in Ketring Park in Littleton. It is edible but has a very strong flavor. No odor but discolors reddish brown.
6. Agaricus "Downing Street:" A large, purple-brown, fibrillose fungi found several times on Downing south of I-25. It grows in the strip between the street and the sidewalk, smells bad, and stains dark red. Most likely related to A. Hondensis and should be considered poisonous.
7. Agaricus "Gary Pickett:" A large, delicious mushroom that grows in Alamo Park in the mulch. Has no odor and does not stain. Gary Picket swears that he dropped his domestic mushroom trimmings in the park and that these beauties were the result.

As the season marches into August and September, the late summer high country thunderstorms work their magic and the Mountain Agaricus begin to appear. They share the same genus characteristics of their city relatives--free gills, chocolate spores, veils and similar staining reactions and odors. Few city mushrooms are found in the mountains; few mountain mushrooms are found in the city with the exception of A. campestris and possibly A. praeclarosquamous. In the mountains at approximately the elevation of Evergreen and above, Agaricus grow in habitats that have much in common with their city counterparts. They like open, grassy fields, conifer duff and squirrel middens, edges, and interfaces between forest and fields. They don't usually grow in rocky areas, near streams or on the bare dirt of trails. Remember, they are saprophytic, not mychorrizal, and need organic matter on which to grow. They are usually solitary, but may sometimes grow in groups of two or three.

The most common Agaricus in dark conifer areas is A. Albolutescens, a fungi that stains obviously amber especially on the cap and smells very strongly of almonds. Edible and a favorite of many, A. sylvicola, another yellow stainer whose counterpart in the city is A. arvensis, grows in mixed aspen/conifer and is usually solitary. It has an anise or licorice odor and is edible.

A. Augustus is a supremely delicious but unfortunately rare mushroom often grows near paths or in disturbed soil and seems to enjoy the sun. The cap and the stalk below the veil are covered with golden brown scales or fibrils. It has a sweet almond smell and stains yellow.
A. osecanus is a robust fungus of fields and foothills, shines like a headlight, and is therefore visible at great distances. It can look like a puffball. The stalk is shaggy below the veil; it stains yellow, and smells like almond. This is one very delicious mushroom if you can find it. There is one bad guy that appears infrequently in the mountains between 7,000 and 9,000 feet usually along roads or in disturbed earth and in great quantities.
The mushroom, A. praeclarosquamous, has dark grey fibrils on the cap stains yellow at the base, smells awful, and looks mean. This could be the A. 'Downing Street' described in June Spores.

We occasionally stumble on Agaricus that stain red and have an almond odor. Once more, we can follow our simple rule: we may eat with caution any Agaricus that does not smell of chemicals. The red stainers growing in Colorado include A fuscofibrillosus, A. pattersonae, and A. sylvaticus. All are edible.

Agaricus do not favor lodgepole, but any area with lots of blue spruce, engelmann spruce or fir is a good place to look for them; they are big, bold mushrooms and very easy to find. I like to look in the deep, dark of the woods of the Chicago Forks area, Guanella Pass Campground and the campgrounds on the east side of Berthoud Pass. They can also grow at high altitude, and I have found some intriguing, though unnamed, collections in Church Park and the Montezuma area. Most Agaricus are exceptionally good to eat and may be cooked using any recipe for supermarket or domestic mushrooms. I prefer to discard the stems because they are tough and have a peculiar flavor. I have also not found a good way to preserve Agaricus; they do not dry particularly well and tend to get flabby when they are frozen. Pickled buttons are good, but my favorite concoctions include A. arvensis pizza with Fontina cheese and sage and marinated, grilled caps of any large, edible Agaricus species. Try these big beauties and I know you will like them.

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