Hydnellum ferrugineum, commonly known as the mealy tooth or the reddish-brown corky spine fungus, is a species of tooth fungus in the family Bankeraceae. A widely distributed species, it is found in north Africa, Asia, Europe, and North America. The fungus fruits on the ground singly or in clusters in conifer forest, usually in poor (low nutrient) or sandy soil. Fruit bodies are somewhat top-shaped, measuring in diameter. Their velvety surfaces, initially white to pink, sometimes exude drops of red liquid. The lower surface of the fruit body features white to reddish-brown spines up to 6 mm long. Mature fruit bodies become dark reddish brown in color, and are then difficult to distinguish from other similar Hydnellum species. H. ferrugineum forms a mat of mycelia in the humus and upper soil where it grows. The presence of the fungus changes the characteristics of the soil, making it more podzolized. Taxonomy The species was originally described scientifically by Elias Magnus Fries, who named it Hydnum ferrugineum in 1815. Its taxonomic history includes transfers to the genera Calodon by Petter Karsten in 1881, and Phaeodon by Joseph Schröter in 1888. It was assigned its current binomial name by Karsten when he transferred it to its current genus, Hydnellum, in 1879. In 1964, Canadian mycologist Kenneth A. Harrison described a hydnoid fungus found with Pinus resinosa in Michigan and Pinus banksiana in Nova Scotia. The fungus, which Harrison named Hydnellum pineticola, is considered to be synonymous with Hydnellum ferrugineum by the nomenclatural database Index Fungorum. Harrison noted "The attempts to recognize European species in North American collections has only increased the confusion in this country, and until someone has worked critically in the field on both continents, it is better to make a recognizable grouping of our own population as that to guess that they may be the same as those that grow in Europe." Other taxa considered synonymous with H. ferrugineum are Pierre Bulliard's 1791 Hydnum hybridum (including later synonyms Calodon hybridus (Bull.) Lindau, and Hydnellum hybridum (Bull.) Banker); Louis Secretan's Hydnum carbunculus (1833); and Howard James Banker's 1906 Hydnellum sanguinarium. Banker explained the difficulty in identifying old Hydnellum specimens: "A considerable number of collections have had to be set aside, as in the dried state, with no notes on the fresh characters, it was impossible to decide with any degree of satisfaction whether the plants represented H. sanguinarium, H. concrescens, H.