| Hydnellum aurantiacum | |
|---|---|
| Scientific classification | |
| Kingdom: | Fungi |
| Phylum: | Basidiomycota |
| Class: | Agaricomycetes |
| Order: | Thelephorales |
| Family: | Bankeraceae |
| Genus: | Hydnellum |
| Species: | H. aurantiacum |
| Binomial name | |
| Hydnellum aurantiacum (Batsch) P. Karst. (1879) |
|
Hydnellum aurantiacum is an inedible fungus, commonly known as the orange tooth or orange Hydnellum for its reddish orange or rusty red colored fruiting bodies. Like other tooth fungi, it bears a layer of spines rather than gills on the underside of the cap. Due to substantial declines in sightings, this species is listed as critically endangered in the United Kingdom.[1][2]
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Hydnellum aurantiacum was first described by the German naturalist August Batsch in 1789, before being given its current scientific name by Petter Karsten in 1879. Its specific epithet aurantiacum is derived from the Latin for "orange".
Fruitbodies are shallowly funnel-shaped (infundibuliform), and up to 15 cm in diameter. The upper surface is orange or orange-brown in the centre, with a lighter margin. It may be velvety or tomentose when young, but will become wrinkled or lumpy in age. The flesh is tough and woody, pale to dark orange-brown in color, without any distinctive odor but a bitter or mealy taste.[3] The teeth are short (up to 5 mm long), white, but the tips gradually turn brown with age. The stipe is up to 4 cm long and 0.5–2 cm thick, orange to dark brown in color, with a velvety surface.[4] The spore print is brown. This species is inedible, due to the toughness of the flesh.
Basidia (the spore-bearing cells) are between 35–46 x 8–11 µm, club-shaped (clavate), without clamp connections, and four-spored. The sterigmata (extensions of the basidia bearing spores) may be up to 6 µm long. Basidiospores are roughly spherical in shape, with rough warty outgrowths (tubercles), nonamyloid, and have dimensions of 5.5–8 x 5.5–6.5 µm.[5]
This species is typically found growing solitary or in clusters on the ground in conifer and mixed woods. Rarely, fruiting bodies may have their stipes fused together.[6]
The orange Hydnellum resembles the polypore Phaeolus schweinitzii when viewed from the top of the pileus surface, but it has teeth instead of pores on the hymenium. Closely related and morphologically similar species in the genus Hydnellum include H. complectipes (fusing of stipes more prevalent), H. congenum (has thin flesh in the pileus), H. ferrugipes and H. earlianum (has a smoother cap, and spines have sulphur yellow tips, not white).[7][8]
The pigment responsible for the characteristic orange color of H. aurantiacum has been identified as the p-terphenyl compound named aurantiacin.[9] The compound dihydroaurantiacin dibenzoate has also been reported.[10]