Lobster mushroom

Hypomyces lactifluorum

The Lobster mushroom, ''Hypomyces lactifluorum'', contrary to its common name, is not a mushroom, but rather 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.
Lobster Mushroom - Hypomyces lactifluorum Fruiting body was hard, orange, ridged, and oddly shaped. It was covered with tiny, orange pimples. The "lobster mushroom" is actually a fungus that has parasitized a Russula or Lactarius mushroom. 

Habitat: Growing on the ground, amid moss in a coniferous forest.
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Behavior

''H. lactifluorum'' specifically attacks members of the genera ''Lactarius'' and ''Lactifluus'' , and ''Russula'' , such as ''Russula brevipes'' and ''Lactifluus piperatus'' in North America. At maturity, ''H. lactifluorum'' thoroughly covers its host, rendering it unidentifiable. Lobster mushrooms are widely eaten and enjoyed; they are commercially marketed and are commonly found in some large grocery stores. They have a seafood-like flavor and a firm, dense texture. According to some, they may taste somewhat spicy if the host mushroom is an acrid ''Lactarius''.

References:

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Taxonomy
KingdomFungi
DivisionAscomycota
ClassSordariomycetes
OrderHypocreales
FamilyHypocreaceae
GenusHypomyces
SpeciesH. lactifluorum