{{Short description|Species of mushroom-forming fungus}} {{Use dmy dates|date=April 2025}} {{Use Oxford spelling|date=April 2025}} {{Speciesbox | image = | image_caption = | taxon = Hydnellum lepidum | authority = (Maas Geest.) E.Larss., K.H.Larss. & Kõljalg<ref name="Larsson et al. 2019"/> | synonyms_ref = <ref name="Ryvarden 2024"/> | synonyms = * ''Sarcodon lepidus'' {{au|Maas Geest. (1975)}} * ''Sarcodon regalis'' {{au|Maas Geest. (1976)}} }}

'''''Hydnellum lepidum''''' is a species of tooth fungus in the family Bankeraceae.<ref name="CoL_6MHHK"/> Found in Europe, it produces pinkish‑brown to purplish‑brown fruiting bodies with scaly caps up to 10&nbsp;cm across and downward‑pointing spines underneath. The fungus forms mycorrhizal associations with deciduous trees, particularly oak.

==Taxonomy==

The fungs was described as new to science in 1975 by the Dutch mycologist Rudolph Arnold Maas Geesteranus.<ref name="Maas Geesteranus 1975"/>

Molecular studies have confirmed that ''Hydnellum lepidum'' belongs in Maas Geesteranus's sect. ''Scabrosi'' and that ''Sarcodon regalis''—originally described alongside ''S.&nbsp;lepidus''—is in fact conspecific with''H.&nbsp;lepidum'', making ''S.&nbsp;regalis'' a later synonym. Moreover, DNA sequences from collections formerly assigned to ''S.&nbsp;cyrneus and ''H.&nbsp;underwoodii fall within the H.&nbsp;lepidum clade, showing how basidiome morphology and pigmentation alone can mislead and highlighting the importance of combining careful macroscopic observation with molecular data for reliable species delimitation.<ref name="Nitare et al. 2021"/>

==Description==

''Hydnellum lepidum'' produces stalked fruit bodies (basidiocarps) that may occur singly or in small groups, sometimes with adjacent caps fusing together (concrescent). The cap (pileus) spans 5–10&nbsp;cm in diameter and is initially flat to slightly convex, becoming gently depressed at the centre in age. Young caps are clothed in a fine, woolly down (tomentose), which soon wears away to leave a surface that is fibrous (fibrillose) and scaly—especially towards the centre. Colouration begins as pinkish‑brown and deepens to purplish‑brown with maturity.<ref name="Ryvarden 2024"/>

Beneath the cap, the hymenophore (fertile spore-bearing surface) bears downward‑pointing spines (teeth) up to 3&nbsp;mm long that run down the stipe (decurrent). These spines start off pale and soon take on a purplish‑brown hue. The flesh (context) of the cap is white and up to 6&nbsp;mm thick at its centre, remaining firm yet slightly fibrous.<ref name="Ryvarden 2024"/>

The stipe reaches 3–4&nbsp;cm in height and 0.5–1.2&nbsp;cm in width, tapering towards the base. It is initially covered in the same fine tomentum as the cap before becoming smooth (glabrous) with age. The stipe matches the cap’s pinkish‑brown tones but often shows a greyish‑green tinge at its base.<ref name="Ryvarden 2024"/>

Under the microscope, the cap tissue comprises simply septate hyphae—thread‑like cells divided by single cross‑walls—up to 24&nbsp;micrometre (μm) wide. The basidiospores are elliptic to irregularly angular or bearing small wart‑like projections (tuberculate), measuring 5.8–6.3 by 3.5–4.3&nbsp;μm, and are pale brown when mature.<ref name="Ryvarden 2024"/>

==Habitat and distribution==

''Hydnellum lepidum'' is widely distributed in Europe, where it forms mycorrhizal associations with deciduous trees, particularly oak (''Quercus''). In Norway, its northern range extends to the southern tip of the country.<ref name="Ryvarden 2024"/>

==References== {{Reflist|refs=

<ref name="CoL_6MHHK">{{Catalogue of Life |id=6MHHK |title=''Hydnellum lepidum'' (Maas Geest.) E. Larss., K.H. Larss. & Kõljalg |access-date=20 April 2025}}</ref>

<ref name="Larsson et al. 2019">{{cite journal |last1=Larsson |first1=Karl-Henrik |last2=Svantesson |first2=Sten |last3=Miscevic |first3=Diana |last4=Kõljalg |first4=Urmas |last5=Larsson |first5=Ellen |title=Reassessment of the generic limits for ''Hydnellum'' and ''Sarcodon'' (Thelephorales, Basidiomycota) |journal=MycoKeys |issue=54 |year=2019 |pmid=31231164 |pmc=6579789 |doi=10.3897/mycokeys.54.35386 |doi-access=free |pages=31–47}}</ref>

<ref name="Maas Geesteranus 1975">{{cite journal |author=Maas Geesteranus RA. |title=Die terrestrischen Stachelpilze Europas |journal=Verhandelingen Koninklijke Nederlandse Akademie van Wetenschappen Afdeling Natuurkunde |year=1975 |volume=65 |series=2 |page=105 |language=de}}</ref>

<ref name="Nitare et al. 2021">{{cite journal |last1=Nitare |first1=J. |last2=Ainsworth |first2=A.M. |last3=Larsson |first3=E. |last4=Parfitt |first4=D. |last5=Suz |first5=L.M. |last6=Svantesson |first6=S. |last7=Larsson |first7=K.-H. |title=Four new species of Hydnellum (Thelephorales, Basidiomycota) with a note on ''Sarcodon illudens'' |journal=Fungal Systematics and Evolution |volume=7 |issue=1 |year=2021 |pmid=34124626 |pmc=8165966 |doi=10.3114/fuse.2021.07.12 |doi-access=free |pages=233–254 |url=https://zenodo.org/records/5838834/files/source.pdf}}</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 |page=32}}{{OA}}</ref>

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{{Taxonbar |from1=Q107746774 |from2=Q10661768 |from3=Q10661772}}

lepidum Category:Fungi described in 1975 Category:Fungi of Europe Category:Fungus species