authors have historically considered the two species to be the same; molecular studies, however, indicate that the two fungi are closely related, but distinct. In contrast with H. ferrugineum, H. spongiosipes has a darker cap when young, darker flesh, and occurs in deciduous woods. Old fruit bodies of H. ferrugineum can be confused with those of Hydnellum concrescens. Habitat and distribution Hydnellum ferrugineum is found mainly in coniferous woodland, often near pines, but occasionally with spruce. Fruit bodies have a preference for sandy soil with low levels of organic matter and nutrients, and grow singly or in clusters. They are more likely to be found in older-growth forests. The fungus occurs in North America, including Mexico. It is widespread but generally uncommon throughout Europe, although there may be local areas where it is common. In Britain, H. ferrugineum is provisionally classified as endangered, and is protected under the Wildlife and Countryside Act 1981; it was included as one of 14 species considered in the United Kingdom Biodiversity Action Plan for stipitate hydnoid fungi (i.e., hydnoid fungi with a cap and stipe) in 2004. The fungus is protected in Montenegro. It has been collected in India and North Africa. The fungus forms a tough mat of mycelia in the humus and upper soil of pine forests. This mycelial mat grows larger with old trees, and can cover an area of several square meters. These areas generally lack dwarf shrubs and promote the vigorous growth of mosses; reindeer lichens often occur in the center of large mats. The presence of the fungus changes the nature of the soil, resulting in a thinner humus layer, decreased groundwater penetration, decreased soil pH, and increases in the level of root respiration as well as the quantity of roots. The fungus also decreases the organic carbon and nitrogen concentrations. Soil with the mycelium becomes more podzolized than the surrounding soil. Similar to some other Hydnellum species, H. ferrugineum is sensitive to the increased nitrogen deposition resulting from clear-cutting, a forestry practice used in some areas of Europe. The fungus forms an unusual type of mycorrhiza with Scots pine (Pinus sylvestris) in which the ectomycorrhiza appears normal at the leading edge of the mycelial mat, but leaves behind dead and atrophied roots at the trailing edge, showing saprophytic tendencies. Bioactive compounds Hydnellum ferrugineum fruit bodies contain the pigments hydnuferrigin (dark violet) and hydnuferruginin (yellow), as well as