Behold the lobster mushroom. Or, more accurately, behold the orange moldy stuff surrounding a mushroom! Named for their distinctive orange color, lobster mushrooms can be found pushing their way up from under the duff in forests after a rain when the humidity is high. Is it a mushroom? Is it a mold? It's both.
Hypomyces lactifluorum
The lobster mushroom consists of two fungi masquerading as one. The part that gives the lobster its color (and hence its name) is Hypomyces lactifluorum. Members of the genus Hypomyces are ascomycetes that grow parasitically on the fruiting bodies of other fungi. They are rather specific in their preference for growing on basidiomycetes. Hypomyces doesn't form mushrooms at all, but produces sexually derived spores in ascocarps called perithecia that are embedded in the orange/red colored stroma surrounding the host mushroom.
Lobster Mushroom and Their Host Species
Hypomyces lactifluorum doesn't parasitize just any old mushroom it happens to come across. It specifically attacks members of the basidiomycete genera Russula and Lactarius, with Russula brevipes and Lactarius piperatus being most commonly found. An exact identification of the host can't always be made.
Orange to red or yellowish colored moldy growths found on other kinds of basidiomyctes, notably some polypores and boletes, are probably Hypomyces species, but not Hypomyces lactifluorum. Lobster mushrooms can be found throughout most of the United States in areas where conditions are good for the host species. Since Russulas and Lactarius are found in pine or mixed wooded areas, that is where you will find lobster mushrooms. If conditions are just right for mushroom formation by the host species, they can be quite common.
Is a Lobster Mushroom Edible?
Hypomyces lactifluorum itself is known to be edible and tastes good according to some. The question takes on a further dimension though, because the mushroom that it is growing on must be considered. Things get complicated by the fact that it isn't easy to identify a mushroom that is blanketed by the orange tissue of a completely different species. However, since Hypomyces lactifluorum is specific in its preference for Russula and Lactarius species, it is generally considered safe. This is because there are no known deadly poisonous species in either of these genera.
This does not mean that all Lactarius and Russula are edible -- they aren't. Some can make the consumer sick and others simply taste bad. There are no reported fatalities from eating lobster mushrooms.
References
Tom Volk's Fungus of the Month for August 2001
Hypomyces lactifluorum, the Lobster Mushroom
Philip McIntosh - The author holds a B.Sc. in Botany and Chemistry and an M.A in Biology and he has thirty + years of experience in science and industry.
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