Hypomyces fungus

Mystery mushroom; turned out to be Battarrea phalloides, July 28, 2019

Mystery Mushroom

In July, a big mushroom popped up close to my garden shed. That was weird, because July isn’t a month in which mushrooms are expected. While not as dry as usual, this July wasn’t exactly rainy, and this fungus was in an especially dry spot. I never water this area and it’s under the shed’s eaves so isn’t exposed to rain. There are odd bits of lumber stashed under the shed, and who knows what might be buried underground. (I know for sure there’s a dead crow a couple feet over and down. I buried it there after finding it one morning. But that was at least ten years ago.)

Looking the mushroom over without disturbing it, I thought it was some kind of Boletus. I saw no gills on the underside of the cap. When I tapped it, rusty brown spores flew out. I checked my mushroom ID books but failed to pin it down to a specific Boletus. I took a picture of it on July 28th (the one at the top of the post) and left it alone.

Usually, mushrooms last a few days and vanish. Not this one. It has remained, looking much the same for more than two months. Finally, a few days ago, I pulled it up. Weirdly, the stipe was attached to a great big cup (called a volva by mycologists) that had been lurking below ground level.

Mystery mushroom, possibly Amanita infected with Hypomyces hyalinus? October 10, 2019
This is how the poor thing looked when I pulled it up on October 10th. Note the cup at the bottom.

Well. This really made me wonder. I wasn’t aware of any Boletus that starts out with a universal veil, a kind of egg-like covering from which some mushrooms grow. The bottom half remains in the ground as a volva and the top part sometimes forms white spots on the mushroom’s cap.

White spots on the cap. Everyone’s seen red mushrooms with white spots, if only in storybooks. Last fall, I had one in the garden, under the birch tree nearly 50 feet away from the shed.

Amanita muscaria mushroom at foot of birch tree
Fly agaric (Amanita muscaria), fall of 2018.

But that’s an Amanita, not a Boletus. Amanitas have gills, not pores. My mystery mushroom certainly didn’t have gills, and if it had pores, they were invisible. The underside of the cap was pure white and smooth.

Forget the books, try Google. I started thinking maybe this mushroom was actually an Amanita that had been parasitized by another fungus. I was aware of the so-called Lobster Mushroom, which is a Russula infected by an organism called Hypomyces lactifluorum. So I started with that and eventually found Hypomyces hyalinus, otherwise known as Amanita mold. Bingo!

Amanita mold “obliterates” the gills of its host and is described as “pallid when old, or tinged with pink, yellow, or brown.” That certainly describes the mystery mushroom. The strange thing is how it’s managed to retain a recognizable shape for more than two months. Perhaps the invading Hypomyces organism replaces the original structures, turning the Amanita into a kind of fungal zombie?

Nature never ceases to amaze.