100 Species #47: Whitish pluteus

This was one of three Pluteus mushrooms that came up together, next to the driveway, photographed on May second.

I've probably stated this here before, but mushroom identification can be very difficult. I could tell right away that this medium sized, dull colored, generally indistinguished set of fungal fruiting bodies was going to be trouble. Still, the opportunity to begin cataloging the wild fungi found in my yard was exciting, so I collected one and began to notice its characteristics.

Color of the cap and step are the first thing you usually notice--in this case more or less whitish, with some brownish discoloration on the top. Then, if you are collecting a specimen, you should dig around the base and get the whole thing--doing this I noticed that the base was swollen and clublike. In hand, you can easily see the color of the gills or "lamellae;" these were also whitish. Most importantly, however, I noticed that the gills did not reach all the way to the stem (do not touch the stem at the center of the mushroom). This condition is called "free gills" and relatively few mushrooms have it. This narrowed it down quite a bit, and Alexis and I looked at some pictures of some candidates, and read some habitat descriptions.

The closest match was Pluteus petasatus, a species not even interesting enough to make it into most of the field guides. If it was there, it was listed as a relative of the deer mushroom Pluteus cervinus which is darker brown on top, and sometimes collected for food. The guides all said that these mushrooms white gills turn pink, and produce a pink spore print. I like making spore prints so I set about to do that a couple days later (my first specimen had been discarded). To my surprise, the remaining mushrooms, in their maturation, were developing pink gills! A good sign to confirm my identification perhaps.

Here's my spore print:


Now, mushroom field guides break spore colors into several different categories, including many (most) that are browns: chocolate brown, ochre, cigar brown, rust brown and so one. I thought this was closest to cigar brown, and was disappointed that it spoiled my identification. Just to be positive, I posted the print to Facebook and tagged it with the names of some people that know A LOT more about mushrooms than I do. (Trust me, one of them literally wrote the book on mushrooms.) The mycologists' verdict? The spore color is "pink," and I should save the spore print and make some others of other colors to compare. Good idea.

Pluteus petasatus is a wood-digesting fungus, but the wood is often hidden below the soil, making it look like the mushrooms are coming directly from the ground. It is a common and widely distributed species, appearing spring to fall, and even winter if it's a warm place. There are several other whitish Pluteus mushrooms that are possible, but may require microscopic examination to eliminate completely. Let's call this identification tentative.

Edited to add: Noah Siegel has shot down the P. petasatus identification; he says "caps fade," meaning that the cap color is not dependable enough to base the ID on--it could be closer to P. cervinus.