Featured Fungus: Cryptoporus volvatus

Oct 27

by Amanda Flaata

A summer trip to the Pacific Northwest—specifically, Gabriola Island off the coast of British Columbia—led me to an unexpected mycological discovery. The forests there were exactly as I imagined—i.e. moss and fern-covered old growth forests of Douglas fir, red cedar, and hemlock. Excited to find a variety of fungi in what appeared to be a lush environment, I was surprised and disheartened to find the landscape parched and fungi few and far between, primarily made up of unremarkable bracket fungi.

Little did I know that this lack of fungi would lead me to a fascinating species that would have otherwise gone unnoticed in a mushroom-filled forest. I happened upon Cryptotporus volvatus, commonly known as the veiled polypore, a species also found in Iowa and associated with conifers.

I first noticed the fungus on a fallen Douglas fir tree (photo 1) in the form of smooth, alabaster, cushion-like masses with orange, black, and purple cracks that reminded me of the veining of marble (photos 2-4). It was beautiful. As I continued down the log, I noticed more masses of different sizes, colors, and textures, each representing a different stage in the fungus’ lifecycle (C. volvatus usually develops the year after a tree’s death, oftentimes at the hands of bark beetles) (photos 5-8). When I touched one of these mature basidiocarps (i.e. spore-bearing fruiting bodies), the top portion was hard and the lower half yielded under the pressure of my thumb; much to my surprise, it was a pliable air-filled pocket with a hole at its base (photo 9). I peered inside the hole and, also to my amazement, saw a brown pore surface (photo 10). What superficially resembled a puffball (e.g. Lycoperdon pyriforme) or even Lycogala slime mold was, in fact, a polypore! A cross-section with a knife confirmed an internal layer of tubes (photos 11-12).

The most intriguing feature of Cryptoporus volvatus is that the pores are covered by a volva-like covering, an unusual evolutionary and reproductive development. Cryptoporus, in fact, means “with secret or hidden pores” and volvatus means "with a volva." One can see a seam, if you will, on the fruiting body where the volva-like tissue extends below the hymenium or spore-bearing surface (photos 13-14). This lower membrane creates a cavity under the hymenium and, as the fungus matures, the spores are released and trapped within this chamber.

This unique structure begs the question—evolutionarily speaking, why cover the pore surface with a volva-like membrane at all? One theory suggests that it retains moisture for spore production during dry seasons (Harrington 1980). Another theory, which has gained traction among scientists in recent years, expounds that it is an adaptation to disperse spores through insect movement (i.e. fungus–insect mutualism) (Kadowaki 2010 and Park et al. 2014).

Unlike other polypores that depend on gravity, wind, and airflows to disperse their spores, Cryptoporus volvatus is at the mercy of coleopteran species, namely beetles, to get the job done. At maturity, an opening develops, what Michael Kuo calls a “trap door”, on the underside of the fungus’ volva-like tissue (Kuo 2023) (photo 9). Lured by an irresistible odor, wood-boring beetles then take shelter, feed, and/or lay eggs within this chamber. Upon exiting, high densities of C. volvatus spores are then carried on their bodies and subsequently dispersed on the next dead tree.

Evidence for fungus-insect mutualism is strong. Cryptoporus volvatus colonizes dead trees that are oftentimes killed by bark beetles; basidiocarps of the fungus, in fact, grow from the bore holes of such beetles. As discussed above, several other beetle species are known to live within and interact with the basidiocarps through mycophagy or egg laying (a few coleopteran species that interact with Cryptoporus volvatus have also been found under the bark of dead conifers, inadvertently passing spores onto bark beetles, which kill the trees, but do not feed or breed within the fruiting bodies). Finally, the fungus has been cultured from the bodies of flying beetles. The propagation and survival of Cryptoporus volvatus is dependent on the movement of a diverse network of coleopteran species.

The beauty of Cryptoporus volvatus is in its evolution to include “secret or hidden pores” to facilitate a symbiotic relationship with insects, among which several species are involved. When encountering the unusual orange or alabaster, marble-veined cushion-like fruiting bodies of C. volvatus in a coniferous forest, pause to reflect on the singularity of its form in the world of fungi.