Hydnellum ferrugineum

Description
Mushroom Identification
Look-Alikes
History
Hydnellum ferrugineum Bioactive Compounds

Description

Hydnellum ferrugineum 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. It is 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 3–10 cm (1–4 in) 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.

Common names: Mealy Tooth, Reddish-Brown Corky Spine Fungus.

Mushroom Identification

Fruit Bodies

The fruit bodies are more or less top-shaped with caps that are 3–10 cm (1.2–3.9 in) in diameter. They are at first convex, then pulvinate (cushion-shaped), later flattening or becoming slightly depressed in the center. Fruit bodies can envelop obstacles as they grow.
Cap

The cap surface of young fruit bodies is uneven, with a velvety to felted texture, and a whitish to pink color. It sometimes exudes blood-red drops of fluid in the depressions. The surface later becomes flesh-colored to dark reddish-brown, but with wavy margin remaining whitish. The lower surface of the fruit body bears the hymenium, the fertile spore-bearing tissue. It comprises a dense arrangement of white to reddish-brown spines up to 6 mm long, hanging vertically downwards.
Stout Stipe

The stout stipe measures 1–6 cm (0.4–2.4 in) long by 1–3 cm (0.4–1.2 in) thick and is the same color as the cap. Fruit bodies have a "distinctly mealy" odor (similar to the smell of freshly ground flour), but are inedible.
Flesh

The flesh is reddish or purplish-brown with white flecks. Initially spongy and soft, it becomes tough and corky as the fruit body matures. In the stipe, the flesh can become blackish in age. Like other Hydnellum species, fruit body tissue is made of generative hyphae that do not expand. This slows the growth of the fruit body, often enabling it to persist for several months.
Spores

The broadly ellipsoid to roughly spherical spores are 5.5–7.5 by 4.5–5.5 μm. Their surfaces are covered with small rounded bumps. The basidia (spore-bearing cells) are narrowly club-shaped, four-spored, and measure 25–30 by 6–7.5 μm. The hyphae of the flesh are brownish with thin walls, and measure 4–6 μm; hyphae in the spines are thin-walled, septate, and sometimes branched, measuring 3.5–4.5 μm. The hyphae do not have clamp connections.

Look-Alikes

Hydnellum peckii

Similar in appearance, but has an acrid taste, and clamp connections in its hyphae.
Hydnellum spongiosipes

Readily confused with H. ferrugineum, and several 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.
Hydnellum concrescens

Old fruit bodies of H. ferrugineum can be confused with H. concrescens.

History

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. scrobiculatum, or some undescribed form."

Common names given to the species include the "reddish-brown corky spine fungus", and the British Mycological Society-sanctioned name "mealy fungus". The specific epithet ferrugineum is Latin for "rust-colored".