Hydnellum aurantiacum

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***Hydnellum aurantiacum*** is an inedible fungus, commonly known as the **orange spine** or **orange Hydnellum** for its reddish orange or rusty red colored fruit 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.

## Taxonomy

*Hydnellum aurantiacum* was first described by the German naturalist August Batsch in 1789, with the name *Hydnum suberosum* var. *aurantiacum*. It was given its current scientific name by Petter Karsten, who transferred it to *Hydnellum* in 1879. *Hydnellum aurantiacum* has acquired several synonyms in its taxonomic history, including *Hydnum stohlii*, published by Gottlob Ludwig Rabenhorst in 1873, and *Hydnellum complectipes*, published by Hall in 1972. Additional synonyms resulting from generic transfers include *Hydnum aurantiacum* (Johannes Baptista von Albertini and Lewis David de Schweinitz, 1825); *Calodon aurantiacus* (Karsten, 1881); and *Phaeodon aurantiacus* (Joseph Schröter, 1888).

The specific epithet *aurantiacum* is derived from the Latin for "orange". Common names for the fungus include "orange spine", "orange corky spine fungus", and the British Mycological Society approved English name "orange Hydnellum".

## Description

 File:2014-08-02 Hydnellum aurantiacum (Batsch) P. Karst 441901.jpg
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. 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. 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 by 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 by 5.5–6.5 µm.

### Similar species

The orange Hydnellum resembles the polypore *Phaeolus schweinitzii* when viewed from the top of the cap surface, but it has teeth instead of pores on the hymenium. Closely related and morphologically similar species in the genus *Hydnellum* include *H. congenum* (has thin flesh in the cap), *H. ferrugipes* and *H. earlianum* (has a smoother cap, and spines have sulfur-yellow tips, not white).

## Distribution and habitat

This species is typically found growing solitary or in clusters on the ground in conifer and mixed woods. Rarely, fruit bodies may have their stipes fused together. *Hydnellum aurantiacum* has been reported from Australia, Europe, North America, and Asia, including China India, and Korea. It is one of the most frequently encountered Thelephorales species found in the Sverdlovsk region of Russia.

## Chemistry

 File:Aurantiacin.svg
The pigment responsible for the characteristic orange color of *H. aurantiacum* has been identified as the *p*-terphenyl compound named aurantiacin. This dark red pigment, a derivative of the compound atromentin, has subsequently been identified in other species of *Hydnellum*. The compounds dihydroaurantiacin dibenzoate and thelephoric acid have also been reported.

*Hydnellum aurantiacum* is used in mushroom dyeing, in which it produces grayish to greenish-gray colors depending on the mordant used.

## References

1. ↑ Trees for Life - Species Profile: Pinewood tooth fungi. Retrieved on January 5, 2009.
2. ↑ Action plan for Grouped plan for tooth fungi. Archived from the original on October 8, 2008. Retrieved on January 5, 2009.
3. ↑ Cite error: Invalid `<ref>` tag; no text was provided for refs named `Batsch 1789`
4. ↑ Cite error: Invalid `<ref>` tag; no text was provided for refs named `Karsten 1879`
5. ↑ 5.0 5.1 Cite error: Invalid `<ref>` tag; no text was provided for refs named `Hall 1972`
6. ↑ Cite error: Invalid `<ref>` tag; no text was provided for refs named `urlFungorum synonymy: Hydnellum aurantiacum`
7. ↑ 7.0 7.1 Cite error: Invalid `<ref>` tag; no text was provided for refs named `McKnight 1987`
8. ↑ Cite error: Invalid `<ref>` tag; no text was provided for refs named `Pegler 1997`
9. ↑ Cite error: Invalid `<ref>` tag; no text was provided for refs named `BMS common names`
10. ↑ Cite error: Invalid `<ref>` tag; no text was provided for refs named `Orr 1980`
11. ↑ Cite error: Invalid `<ref>` tag; no text was provided for refs named `Ellis 1990`
12. ↑ Cite error: Invalid `<ref>` tag; no text was provided for refs named `Baird 1986`
13. ↑ Cite error: Invalid `<ref>` tag; no text was provided for refs named `Arora 1986`
14. ↑ Cite error: Invalid `<ref>` tag; no text was provided for refs named `May 2003`
15. ↑ Cite error: Invalid `<ref>` tag; no text was provided for refs named `Miller 2006`
16. ↑ Cite error: Invalid `<ref>` tag; no text was provided for refs named `Dai 2010`
17. ↑ Cite error: Invalid `<ref>` tag; no text was provided for refs named `Lyngdoh 2014`
18. ↑ Cite error: Invalid `<ref>` tag; no text was provided for refs named `Lee 2005`
19. ↑ Cite error: Invalid `<ref>` tag; no text was provided for refs named `Shiryaev 2008`
20. ↑ Cite error: Invalid `<ref>` tag; no text was provided for refs named `Gripenberg 1956`
21. ↑ Cite error: Invalid `<ref>` tag; no text was provided for refs named `Velíšek 2011`
22. ↑ Cite error: Invalid `<ref>` tag; no text was provided for refs named `Gripenberg 1958`
23. ↑ Cite error: Invalid `<ref>` tag; no text was provided for refs named `Bessette 2001`

## External links

* Template:IndexFungorum
* Roger's Mushrooms
* Several Photos

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