# Helocarpon

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{{Short description|Genus of lichen-forming fungi}}
{{Use dmy dates|date=February 2026}}
{{Use Oxford spelling|date=February 2026}}
{{Automatic taxobox
| image = Leimonis erratica 597551.jpg
| image_caption = ''Helocarpon erraticum''
| taxon = Helocarpon
| authority = [Th.Fr.](/source/Th.Fr.) (1860)
| type_species = ''Helocarpon crassipes''
| type_species_authority = Th.Fr. (1860)
| subdivision_ranks = Species
| subdivision = ''[H. assimilatum](/source/Helocarpon_assimilatum)''<br />
''[H. crassipes](/source/Helocarpon_crassipes)''<br />
''[H. erraticum](/source/Helocarpon_erraticum)''<br />
''[H. paratropum](/source/Helocarpon_paratropum)''
| synonyms_ref = <ref name="Myllys et al. 2026"/><ref name="Harris 2009"/>
| synonyms = *''Leimonis'' {{au|R.C.Harris (2009)}}
}}

'''''Helocarpon''''' is a [genus](/source/genus) of [lichen](/source/lichen)-forming [fungi](/source/fungi) in the family [Ectolechiaceae](/source/Ectolechiaceae). It contains a small number of [crustose](/source/crustose_lichen) species that occur mainly in cool, northern and [montane](/source/montane) environments, where they grow on soil or rock. The genus is closely related to ''[Micarea](/source/Micarea)'', but differs in a suite of [morphological](/source/morphology_(biology)) traits and is treated as a distinct [lineage](/source/lineage_(evolution)) in modern multilocus classifications. Species in the genus are associated with cool climates and are found mainly in [arctic](/source/arctic_climate), [subarctic](/source/subarctic), and [alpine](/source/alpine_climate) regions, where they grow on soil or rock. The genus was proposed by [Theodor Magnus Fries](/source/Theodor_Magnus_Fries) in 1860, and a major [molecular](/source/molecular_phylogenetics) study published in 2026 confirmed it as a distinct [lineage](/source/lineage_(evolution)) separate from ''Micarea''.

==Taxonomy==
''Helocarpon'' was established by [Theodor Magnus Fries](/source/Theodor_Magnus_Fries) in 1860, with ''H.&nbsp;crassipes'' assigned as the [type species](/source/type_species).<ref name="Myllys et al. 2026"/> Its placement has shifted between classifications. In [morphology](/source/morphology_(biology))-based systems its wider relationships were uncertain, and [Josef Hafellner](/source/Josef_Hafellner) introduced the monogeneric family Helocarpaceae in 1984 to accommodate the genus.<ref name="Hafellner 1984"/> Some later outline classifications instead placed ''Helocarpon'' in Micareaceae alongside ''Micarea'' and other superficially similar crustose lichens.<ref name="Eriksson et al. 2004"/>

Authors also differed on [rank](/source/taxonomic_rank) and [circumscription](/source/circumscription_(taxonomy)): some retained ''Helocarpon'' as a distinct genus, whereas others treated it within a broad ''[Micarea](/source/Micarea)'' concept (for example, in a European revision that grouped ''H.&nbsp;crassipes'' with morphologically similar ''Micarea'' species).<ref name="Coppins 1983"/><ref name="Myllys et al. 2026"/> Early [molecular](/source/molecular_phylogenetics) work added noise rather than clarity because a mitochondrial-[rDNA](/source/ribosomal_DNA) sequence attributed to ''H.&nbsp;crassipes'' was later shown to represent a species of ''[Bryobilimbia](/source/Bryobilimbia)''; together with limited taxon sampling, this contributed to conflicting placements in the early literature.<ref name="Andersen & Ekman 2005"/><ref name="Myllys et al. 2026"/>

A comprehensive five-[locus](/source/locus_(genetics)) phylogeny published in 2026 recovered ''Helocarpon'' as a strongly supported [clade](/source/clade) that is [sister](/source/sister_group) to ''Micarea'' in a broad sense, and treated it as a separate genus rather than as the earliest-diverging branch of ''Micarea''.<ref name="Myllys et al. 2026"/> In that treatment, several species long placed in ''Micarea'' were recombined into ''Helocarpon'', and the [monotypic](/source/monotypic) genus ''Leimonis'' (described for the saxicolous ''Lecidea''/''Micarea'' species ''erratica'') was reduced to synonymy with ''Helocarpon''.<ref name="Harris 2009"/><ref name="Myllys et al. 2026"/> Although ''Micarea lynceola'' was transferred to ''Leimonis'' in 2017, the 2026 study did not support ''erratica'' and ''lynceola'' as a monophyletic pair in [mtSSU](/source/mtSSU) analyses and treated ''lynceola'' as part of a separate ''Micarea'' lineage rather than within ''Helocarpon''.<ref name="Myllys et al. 2026"/><ref name="Harris 2009"/><ref name="Aptroot 2017"/> The same study also treated ''Helocarpon pulverulum'' as a synonym of ''H.&nbsp;crassipes'', interpreting it as part of a continuum of thallus development rather than as a separate species.<ref name="Myllys et al. 2026"/>

The 2026 revision discussed additional taxa that might prove related to ''Helocarpon'' but were not formally transferred because of missing or inconclusive data. For example, the placement of ''[Micarea doliiformis](/source/Micarea_doliiformis)'' was treated as unresolved despite an apparent relationship in some single-locus analyses, and other species (such as the North American ''[Micarea subalpina](/source/Micarea_subalpina)'') were flagged as potentially relevant but in need of targeted sampling and sequencing.<ref name="Myllys et al. 2026"/>

==Description==
thumb|right|Closeup of ''Helocarpon crassipes'' showing its black, marginate apothecia; scale: 1 mm
Species of ''Helocarpon'' are [crustose lichen](/source/crustose_lichen)s with a [thallus](/source/thallus) that ranges from thin and poorly developed to well-developed and distinctly {{lichengloss|areolate}}. Compared with many species traditionally placed in ''Micarea'', members of the ''Helocarpon'' lineage tend to have a more conspicuous apothecial margin (a well-developed {{lichengloss|exciple}}) and, in some taxa, relatively large {{lichengloss|photobiont}} cells rather than the paired "micareoid" arrangement common in ''Micarea'' sensu stricto.<ref name="Harris 2009"/><ref name="Myllys et al. 2026"/> [Apothecia](/source/Apothecia) (fruiting bodies) are generally dark (often black), and in the type species they are characteristically shortly stalked and clearly {{lichengloss|marginate}}.<ref name="Myllys et al. 2026"/> Internal pigmentation is often strong in the apothecial tissues (for example, dark {{lichengloss|hypothecium|hypothecial}} colours have been used in traditional species concepts within the group).<ref name="Coppins 1983"/><ref name="Myllys et al. 2026"/>

Some species associate secondarily with [cyanobacteria](/source/cyanobacteria) in addition to their green-algal photobiont. In the [arctic-alpine](/source/arctic-alpine) ''H.&nbsp;assimilatum'', cyanobacteria occur in ''[Nostoc](/source/Nostoc)''-containing [cephalodia](/source/cephalodia), whereas the closely related saxicolous ''H.&nbsp;paratropum'' lacks ''Nostoc'' cephalodia and instead commonly shows ''[Stigonema](/source/Stigonema)'' clusters between the {{lichengloss|areoles}}. Chemically, species in the lineage were characterized in the 2026 revision as lacking detectable [lichen substance](/source/lichen_substance)s in the standard sense used for many ''Micarea'' groups.<ref name="Myllys et al. 2026"/>

==Habitat and distribution==
''Helocarpon'' is most often encountered in cool-climate habitats, especially in [arctic](/source/arctic_climate), [subarctic](/source/subarctic), and [alpine](/source/alpine_climate) or [subalpine](/source/subalpine) environments. Species occur on mineral soil or plant debris on the ground ([terricolous](/source/terricolous_lichen)) as well as directly on rock (saxicolous).<ref name="Myllys et al. 2026"/> In the 2026 synthesis, ''H.&nbsp;crassipes'' and ''H.&nbsp;assimilatum'' were discussed as terricolous species associated with arctic-alpine settings, while ''H.&nbsp;erraticum'' was described as mostly saxicolous and widely distributed.<ref name="Harris 2009"/><ref name="Myllys et al. 2026"/>

The most range-restricted species discussed in detail was ''H.&nbsp;paratropum'', which was treated as an arctic-alpine lichen known from Scotland and [Scandinavia](/source/Scandinavia) and also reported from Canada. It resembles ''H.&nbsp;assimilatum'' morphologically but differs in [substrate](/source/substrate_(biology)) preference and in its cyanobacterial associations.<ref name="Myllys et al. 2026"/>

==Species==
The 2026 multilocus revision recognised four species in ''Helocarpon'':<ref name="Myllys et al. 2026"/>
* ''[Helocarpon assimilatum](/source/Helocarpon_assimilatum)'' {{au|(Nyl.) M.Svenss., Myllys & Kantel. (2026)}}<ref name="Myllys et al. 2026"/>
* ''[Helocarpon crassipes](/source/Helocarpon_crassipes)'' {{au|Th.Fr. (1860)}}<ref name="Fries 1860"/>
* ''[Helocarpon erraticum](/source/Helocarpon_erraticum)'' {{au|(Körb.) M.Svenss., Myllys & Kantel. (2026)}}<ref name="Myllys et al. 2026"/>
* ''[Helocarpon paratropum](/source/Helocarpon_paratropum)'' {{au|(Nyl.) M.Svenss., Myllys & Kantel. (2026)}}<ref name="Myllys et al. 2026"/>

==References==
<references>

<ref name="Andersen & Ekman 2005">{{cite journal |last1=Andersen |first1=Heidi L. |last2=Ekman |first2=Stefan |year=2005 |title=Disintegration of the Micareaceae (lichenized Ascomycota): a molecular phylogeny based on mitochondrial rDNA sequences |journal=Mycological Research |volume=109 |issue=1 |pages=21–30 |doi=10.1017/S0953756204001625 |pmid=15736860}}</ref>

<ref name="Aptroot 2017">{{cite journal |last=Aptroot |first=A. |year=2017 |title=Nomenclatural novelties |journal=Index Fungorum |volume=331 |page=1 |url=https://www.indexfungorum.org/Publications/Index%20Fungorum%20no.331.pdf}}</ref>

<ref name="Coppins 1983">{{cite journal |last=Coppins |first=B.J. |year=1983 |title=A taxonomic study of the lichen genus ''Micarea'' in Europe |journal=Bulletin of the British Museum of Natural History |volume=11 |page=108}}</ref>

<ref name="Eriksson et al. 2004">{{cite journal |last1=Eriksson |first1=O.E. |last2=Baral |first2=H.-O. |last3=Currah |first3=R.S. |last4=Hansen |first4=K. |last5=Kurtzman |first5=C.P. |last6=Rambold |first6=G. |last7=Laessøe |first7=T. |title=Outline of Ascomycota – 2004. |journal=Myconet |year=2004 |volume=10 |pages=1–99}}</ref>

<ref name="Fries 1860">{{cite journal |last=Fries |first=T.M. |year=1860 |title=Lichenes arctoi Europae Groenlandiaeque hactenus cogniti |journal=Nova Acta Regiae Societatis Scientiarum Upsaliensis |series=3 |volume=3 |pages=103–398 [178] |language=la}}</ref>

<ref name="Hafellner 1984">{{cite journal |last1=Hafellner |first1=J. |year=1984 |title=Studien in Richtung einer natürlichen Gliederung der Sammelfamilien Lecanoracae und Lecideaceae |trans-title=Studies towards a natural classification of the collective families Lecanoraceae and Lecideaceae |journal=Beihefte zur Nova Hedwigia |volume=79 |pages=241–371 [285] |language=de}}</ref>

<ref name="Harris 2009">{{cite journal |last=Harris |first=Richard C. |title=Four novel lichen taxa in the lichen biota of eastern North America |journal=Opuscula Philolichenum |volume=6 |year=2009 |doi=10.5962/p.381977 |pages=149–156 |url=https://www.biodiversitylibrary.org/part/381977 |doi-access=free}}</ref>

<ref name="Myllys et al. 2026">{{cite journal |last1=Myllys |first1=Leena |last2=Svensson |first2=Måns |last3=Kantvilas |first3=Gintaras |last4=Sérusiaux |first4=Emmanuel |last5=van den Boom |first5=Pieter |last6=Aptroot |first6=André |last7=Cezanne |first7=Rainer |last8=Eichler |first8=Marion |last9=Pino-Bodas |first9=Raquel |last10=Printzen |first10=Christian |last11=Pykälä |first11=Juha |last12=Thor |first12=Göran |last13=Westberg |first13=Martin |last14=Weber |first14=Lilith |last15=Kantelinen |first15=Annina |title=The first comprehensive multilocus phylogeny of the lichenized genus ''Micarea'' (Ectolechiaceae, Ascomycota) |journal=Taxon |volume=75 |issue=1 |year=2026 |doi=10.1002/tax.70087 |doi-access=free |article-number=e70087}}</ref>

</references>

{{Taxonbar|from=Q10520452}}

Category:Ectolechiaceae
Category:Lecanorales genera
Category:Lichen genera
Category:Taxa named by Theodor Magnus Fries
Category:Taxa described in 1860

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Adapted from the Wikipedia article [Helocarpon](https://en.wikipedia.org/wiki/Helocarpon) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Helocarpon?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.