{{Short description|Species of mushroom-forming fungus}} {{Use dmy dates|date=April 2025}} {{Use Oxford spelling|date=April 2025}} {{Speciesbox | image = Sarcodon fennicus by caspar s.jpg | image_caption = | taxon = Hydnellum fennicum | authority = (P.Karst.) E.Larss., K.H.Larss. & Kõljalg<ref name="Larsson 2019">{{Cite journal|author1=Larsson|author2=Svantesson|author3=Miscevic|author4=Kõljalg|author5=Larsson|date=2019|title=Reassessment of the generic limits for Hydnellum and Sarcodon (Thelephorales, Basidiomycota)|journal=MycoKeys|issue=54|pages=31–47|doi=10.3897/mycokeys.54.35386|pmid=31231164|pmc=6579789 |doi-access=free }}</ref> | synonyms_ref = <ref name="urlFungorum synonymy: Sarcodon fennicus"/> | synonyms = *''Sarcodon scabrosus'' var. ''fennicus'' {{au|P.Karst. (1882)}} *''Hydnum fennicum'' {{au|(P.Karst.) Sacc. (1888)}} *''Phaeodon fennicus'' {{au|(P.Karst.) Henn. (1898)}} *''Hydnellum fennicus'' {{au|(P.Karst.) P.Karst. (1887)}} }}

'''''Hydnellum fennicum''''' is a species of tooth fungus in the family Bankeraceae. Native to northern Europe, it forms mycorrhizal associations with pine trees. It is recognised by its yellowish‑brown cap covered in fine powdery scales and by downward‑pointing teeth beneath that change from whitish to purplish‑brown. The fungus is considered critically endangered in Switzerland due to habitat loss.

==Taxonomy==

It was originally described by the Norwegian mycologist Petter Karsten in 1882 as a variety of ''Sarcodon scabrosus''.<ref name="Karsten 1882"/> Karsten promoted it to a distinct species in 1887.<ref name="Karsten 1887"/>

==Description==

''Hydnellum fennicum'' produces fruit bodies (basidiocarps) that occur singly or in small clusters. The cap (pileus) grows up to 10&nbsp;cm in diameter and often develops a shallow central depression. Its surface is densely covered in fine, powdery scales—those in the centre tending to stand upright, while those towards the margin lie flat. Young caps are ochre‑yellow, but they darken to yellow‑brown over time and may show patches of reddish‑brown. Beneath the cap, the hymenophore is composed of slender, downward‑pointing spines (or "teeth") up to 5&nbsp;mm long; these start off whitish and gradually deepen to purplish‑brown. The flesh (context) is white throughout but shows greenish to greyish tones at the base of the stem (stipe), and emits a faint bitter‑almond smell when fresh.<ref name="Ryvarden 2024"/>

The stipe is cylindrical, measuring 3–7&nbsp;cm tall by 1–3&nbsp;cm thick. It is initially tomentose—that is, clothed in a soft, woolly mat of hairs—but becomes smooth (glabrous) with age. Its colour matches the cap except at the very base, which often turns bluish‑green to greyish‑green and may be overlaid by pale mycelium (the fungal network). Under the microscope, the cap tissue comprises simple septate hyphae—thread‑like cells divided by cross‑walls—up to 20&nbsp;μm wide. The spores formed on the spines (basidiospores) are pale brown, sharply angular in outline, and measure roughly 6.3–7.6 by 4.5–5.2&nbsp;μm.<ref name="Ryvarden 2024"/>

==Habitat and distribution==

''Hydnellum fennicum'' is distributed primarily in continental Norway and eastwards. It forms ectomycorrhizae with pine.<ref name="Ryvarden 2024"/> It is considered critically endangered in Switzerland.<ref name="Senn-Irlet 2007"/>

==References== {{Reflist|refs=

<ref name="Karsten 1882">{{cite journal |last=Karsten |first=P. |title=Rysslands, Finlans och den Skandinaviska halföns Hattsvampar. Sednare Delen: Pip-, Tagg-, Hud-, Klubb- och Gelésvampar |journal=Bidrag till Kännedom av Finlands Natur och Folk |year=1882 |volume=37 |page=104}}</ref>

<ref name="Karsten 1887">{{cite journal |last=Karsten |first=P.A. |title=Fungi novi vel minus bene cogniti Fenniae et Galliae |journal=Revue Mycologique Toulouse |year=1887 |volume=9 |pages=9–11 |language=la}}</ref>

<ref name="Ryvarden 2024">{{cite book |last=Ryvarden |first=Leif |year=2024 |title=Hydnoid Genera – A World Synopsis |series=Synopsis Fungorum |volume=50 |publisher=Fungiflora |location=Oslo |url=https://www.fungiflora.no/synopsis-50-hydnoid-genera}}{{OA}}</ref>

<ref name="Senn-Irlet 2007">{{cite report |last1=Senn-Irlet |first1=B. |last2=Bieri |first2=G. |last3=Egli |first3=S. |title=Lista Rossa Macromiceti. Lista Rossa delle specie minacciate in Svizzera. UV-0718-I |year=2007 |location=Bern |publisher=Ufficio federale dell’ambiente |language=it |url=http://www.bafu.admin.ch/publikationen/publikation/00055/index.html?lang=fr&lang=it}}</ref>

<ref name="urlFungorum synonymy: Sarcodon fennicus">{{cite web |title=GSD Species Synonymy: ''Sarcodon fennicus'' (P. Karst.) P. Karst. |url=https://www.speciesfungorum.org/GSD/GSDspecies.asp?RecordID=222520 |publisher=Species Fungorum. CAB International |access-date=2016-02-04}}</ref>

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{{Taxonbar|from=Q10430338}}

fennicum Category:Fungi described in 1882 Category:Fungi of Europe Category:Inedible fungi Category:Taxa named by Petter Adolf Karsten Category:Fungus species