Weird and Wonderful Wild Mushrooms: Unveiling the Veiled Polypore: Cryptoporus volvatus

I spent an hour this morning carefully destroying fifteen veiled polypores—totally ripped them apart. Odd thing to do? Nope, not in my neck of the woods.

Cryptoporus volvatus produces acorn- to walnut-sized cream-coloured bubbles on the bark of recently dead and usually still standing conifers. Sometimes it also appears on living trees.

C. volvatus grows on recently dead or dying conifers.

At first glance, these cute little polypores might be mistaken for small, wood-inhabiting puffballs, or even the immature fruiting bodies of the slime molds Reticularia lycoperdon or Lycogala reticularia.

Lycoperdon pyriforme Lycogala flavofuscum Reticularia lycoperdon

Cryptoporus volvatus can superficially resemble (left to right)
Lycoperdon pyriforme puffballs (Wikipedia), or immature slime
molds such as Lycogala flavofuscum and Reticularia lycoperdon.

The reason they might not be immediately identifiable as polypores is that their pore surface is hidden, hence the "crypto" part of their name. Unlike other polypores, the spore-producing bottom side of the "veiled polypore" is covered by a volva-like flap of tissue—a covering that would apparently prevent the free movement of spores.

Cryptoporus volvatus openings and lacquer-like coating

Note both the newly formed openings, or ostioles, and the
shedding of the lacquer-like coating (Dan Molter)

So how do these diminutive polypores manage to get their spores out into the larger world? For many years it was assumed that insects and other arthropods that are known to spend time inside these fungi are the obvious vector for spore dispersal. C. volvatus even provides a convenient doorway to gain access: a small ostiole that forms at the juncture with the tree, which enlarges as the spores mature.

The opening at the top of the photo is the ostiole that forms
in the pore covering. The other holes were made by insects.

But a 1980 study cast doubt on the insect link. The paper, published in Mycologia, posited that spore dispersal was primarily via air movement, just as it is for other polypores. The authors came to this conclusion by rigging up a bunch of C. volvatus with spore-collecting contraptions, then suspended the collected spores evenly in a liquid, and finally counted them using a hemocytometer, a gauge invented in the 19th century for blood cells. And they found a lot of escaped spores—an average of 2.5 billion per basidiocarp. That's a lot of spores sent on their way by wind—comparable, in fact, to other polypores.

So why evolve a covered pore surface in the first place? The authors suggest that it has to do with moisture retention. Many polypores are capable of resuming sporulation after they have completely dried out when they are rehydrated by rain. Not the short-lived C. volvatus, which usually grows well above the ground on standing trees where it is open to the desiccating effects of sun and wind. Basically, it's got only one chance to produce spores, so a protective tube covering makes sense.

Cryptoporus volvatus brown shiny lacquer cracks

The lacquer-like coating that covers young C. volvatus

is also thought to help retain moisture.

But that air-movement and spore dispersal study didn't make the people who had a gut feeling that insects still belonged in the equation go away. Nope. This isn't surprising considering the number and variety of mini spelunkers that choose to hang out in dark, spore-covered, Crytoporus caves.

Insects, like this one with metallic red elytra, tuck themselves
tightly into the corners when you remove the covering.

One Japanese study that looked at 438 separate C. volvatus basidiocarps counted a total of 8,990 individuals, insects that belonged to 17 different species, including 4 specialists that prefer C. volvatus over everything else. Some of these little mycophagists munch on the tubes, some eat the flesh, while others focus on the fallen spores. Predators enter as well. Several studies around the world have focussed on these insects and the possibility of their being a necessary vector for spore dispersal.

This sporocarp has been completely hollowed out by insects.

In one Korean study, beetles were collected from C. volvatus basidiocarps and then "vortexed" (what a great verb!) in ethanol to dislodge any spores that were attached to them. Again, a hemocytometer was used to count the spores each insect specimen carried. And they carried a lot: from 10,000 to half a billion. That's a lot of spores to be moving around for no good reason.

Basidiocarps of C. volvatus actually grow out of exit, entrance, and ventilation holes made by bark beetles—bark beetles that kill conifers but that are not known to feed on the fruitbodies of C. volvatus. So how do the spores gain entry to a tree? Air movement can't be enough. But it turns out that at least one species in the Korean study that feeds/breed inside the volval chambers of C. volvatus also spends time under the bark of dead conifers, so it could easily be a vector for spore transfer, perhaps to a passing bark beetle.