Tuesday, August 21, 2012

A mushroom harvest

kw: natural history, fungi

I went out to mow, taking advantage of the spate of nice weather. When I got to the side yard, it didn't take long to run across this big mushroom. Its cap is about 15 cm (6 in) across. It felt woody, more like a bracket fungus (shelf mushroom, like you find on tree trunks) than a "toadstool".

A later search among fungus identification web sites indicated that it is probably a species of Boletellus. Most members of this genus are not edible, but I wouldn't want to eat such a woody mushroom anyway.

When I pulled it out, I found beneath it a dark brown spore print. The spore color helped identify it. I suppose I could also have gathered some spores to check under the microscope. The main way you distinguish among dark-spored Boletellus species is by spore morphology.

Instead, I went around the yard and gathered them all up. They were clearly following the trace of roots of a tree, a sweet gum or Liquidamber, that we removed five years ago. It takes the roots of a cut-down tree years to be convinced that they are dead. At that point, the commensal fungi push up fruiting bodies like these in an effort to propagate wherever the wind blows.

Here is the collection, on the back stoop. I count six mature fruits (two are shown sideways, in back, so their white underside is visible) and fourteen smaller ones. All are quite woody, and it took some effort to break them free from the mycelium underground. The one shown above is on the left.

From a close look at the underside I saw that they have no gills. They have pores instead, but I was hard put to see the pores, they are so small. It was the fine pores that led me to the genus identification. Even though the pores are small, they are quite large enough to drop copious spores, which are less than 10 microns in size. That spore print shown above must contain millions of spores.

The pores look like this at about 10x magnification. The brown object is a piece of weed stem that the mushroom had enveloped as it grew. Compare these tiny pores with the pores of Boletus fraternus, a smaller and softer mushroom with a red cap and yellow underside, that I found growing in a corner of the yard when I was gathering the Boletellus.

I understand that Boletus fraternus is edible. I don't plan to test the notion. I am reasonably certain of my identification, but not enough to stake my health on it!

Here it is, in case someone wants to tell me I got it wrong (or right!).

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