You may have head that the mushroom is only a small part of a fungus, and this is true — a mushroom is a temporary spore-releasing structure, ephemeral like a flower, while the growing, eating part of the fungus is usually hidden away. Here it takes the form of a network of hyphae, thin filaments that branch out into soil, rotting wood, an animal carcass, old cheese or whatever else happens to be the fungus’s purview. The hyphal network is the fungus.
It should come as no surprise, then, that some fungi have evolved that never produce mushrooms. Mycologists sometimes call them “imperfect fungi” — others call them molds. Today’s new species is an imperfect fungus, Talpapellis solorinae, from British Columbia (Zhurbenko et al. 2015). It is not unusual in appearance, but in habits: this fungus is a parasite that lives and grows on the surface of lichens.
Such lichen-eating fungi are termed “lichenicolous.” In this case, the host is the socket lichen (Solorina crocea), a large species that can grow on soil, rocks, tree bark, and a variety of other surfaces. As it grows, the parasite creates velvety black, “moldy” patches on the lichen, which itself is an attractive shade of green.
Lichens are fungi that have formed symbiotic relationships with algae. In this relationship, the fungus provides a protected environment and nutrients for the alga, while the alga turns sunlight into energy that both partners can use. Although lichens are often fleshy and look similar to mushrooms, they are not. Instead, the lichen is formed by above-ground hyphae, densely coiled, woven, and packed into a solid mass.
Many fungi are parasitic, feeding on hosts ranging from insects to plants to humans. Most are extremely specific, only growing on a particular family, genus, or even species of host. The new socket lichen parasite has only been found on one species of lichen. Other closely-related parasites have been found on other species of lichens, but only in a single family Peltigeraceae. Incidentally, Peltigeraceae includes many of the large, attractive lichens we commonly associate with boulders and rock walls.
As with all molds, the velvety, visible layer is covered with single-celled spores. When the wind picks up, it carries these spores and scatters them over the landscape. A lucky few land on or near a socket lichen, and begin the cycle anew.
Ed.: Shortly after I posted this article, I found another recent paper (Westberg et al. 2015) featuring the lichens of Scandinavia along with their fungal parasites. The most interesting of these is the gall-forming Tremella. Tremella fungi are parasites on a wide range of hosts, always other fungi and often lichens. Just like gall-forming insects that manipulate their plant hosts, this species (T. lobariacearum) secretes chemicals that force its lichen host to warp and grow into a gall, a protective structure in which the parasite lives.
Westberg M., E. Timdal, J. Asplund, M. Bendiksby, R. Haugan, F. Jonsson, P. Larsson, G. Odelvik, M. Wedin, A. Millanes. 2015. New records of lichenized and lichenicolous fungi in Scandinavia. MycoKeys 11: 33-61.
Zhurbenko M.P., B. Heuchert, and U. Braun. 2015. Talpapellis solorinae sp. nov. and an updated key to the species of Talpapellis and Verrucocladosporium. Phytotaxa 234(2): 191-194.