Hygrocybe is a genus of colorful agarics in the family Hygrophoraceae or waxcaps. Members of the genus Waxcaps are distinguished from other members of the Hygrophoraceae by their often brightly-colored fruiting bodies, the saprotrophic habitat of most species (though a few have been shown to be ectomycorrhizal), and subparallel to parallel lamellar trama. This genus includes the "witches hats" (Hygrocybe conica and allies), a group of species distinguished by their bright red and yellow fruiting bodies, strong black-staining reaction when handled, and extremely viscid fruiting bodies. Some grassland and heath ecosystems, particularly in Europe, have a great abundance and diversity of Hygrocybe species.
This genus is recognized by some modern authorities and not by others. Hesler and Smith (1963) and Largent (1985) consigned it to sectional rank, Hygrophorus section Hygrocybe, though Largent (1988) later recognized its generic status. Boertmann (1996), also recognizes the generic status of this group and includes species classified by some other authors as Camarophyllus within it.
Some species, such as the mauve splitting waxcap (Humidicutis lewelliniae) of Southeastern Australia, have been described in the small genus Humidicutis.
Source: en.wikipedia.org/wiki/Hygrocybe - 25.06.2010
They grow in the same earth, get the same dosage of sunlight and rain, however one is bright green and the other bright red.