Hypomyces lactifluorum

Hypomyces lactifluorum, or the lobster mushroom, is a parasitic ascomycete fungus that grows on certain species of mushrooms, turning them a reddish orange color that resembles the outer shell of a cooked lobster. Contrary to its common name, the species itself is neither a mushroom nor a crustacean.

Description
H. lactifluorum specifically attacks members of the genera Lactarius and Lactifluus (milk-caps), and Russula (brittlegills), such as Russula brevipes and Lactifluus piperatus in North America. At maturity, the reddish orange H. lactifluorum thoroughly covers its host, rendering it unidentifiable.

The species produces a white spore print.

Similar species
Similar species include Hypomyces cervinigenus, H. chrysospermus, and H. luteovirens. Turbinellus floccosus has a similarly colored cap but its underside has fine wrinkles rather than wavy gills. White, pink and yellow molds could be toxic lookalike species.

Uses
Lobster mushrooms are widely eaten and enjoyed freshly foraged and cooked. They are commercially marketed and sometimes found in grocery stores; they have been made available at markets in Oregon. They have a seafood-like flavor and a firm, dense texture.

While edible, field guides note the hypothetical possibility that H. lactifluorum could parasitize a toxic host and that individuals should avoid consuming lobster mushrooms with unknown hosts, although no instances of toxicity have been recorded. During the course of infection, the chemicals get converted into other more flavorful compounds, making lobster mushrooms more edible. Lactarius piperatus has a spicy, hot flavor but that flavor is counteracted by the parasite H. lactifluorum, making it more edible and delicious. One author notes that he has personally never experienced any trouble from consuming them and another notes that there have been no reports of poisoning in hundreds of years of consumption.

Research
A study from Quebec found that an infected R. brevipes mushroom mostly contained lobster mushroom DNA, with only trace amounts from the original species. This study also measured intermediate products of chemical reactions, or metabolites, in infected and non-infected mushrooms. Metabolites help determine how fungi look and taste, and whether they are fit to eat. They found that through the course of its infection, the parasitic fungus completely alters the diversity and amount of metabolites in R. brevipes.