{{Short description|Genus of lichens}} {{Use dmy dates|date=August 2024}} {{Use British English|date=August 2024}} {{Automatic taxobox | image = | taxon = Leptogidium | authority = Nyl. (1873) | type_species = Leptogidium dendriscum | type_species_authority = (Nyl.) Nyl. (1873) | subdivision_ranks = Species | subdivision = ''L. byssoides''<br /> ''L. contortum''<br /> ''L. dendriscum''<br /> ''L. intricatulum''<br /> ''L. neocaledonicum''<br /> ''L. stipitatum'' }}
'''''Leptogidium''''' is a genus of lichen-forming fungi in the family Pannariaceae.<ref name="Wijayawardene et al. 2022"/> It has six species.<ref name="CoL"/>
==Taxonomy==
The genus was circumscribed by the Finnish lichenologist William Nylander in 1873.<ref name="Nylander 1873"/> It was originally classified within the broader genus ''Polychidium''. However, molecular phylogenetic studies conducted in 2011 revealed that ''Leptogidium'' is a distinct genus, separate from ''Polychidium''. ''Leptogidium'' belongs to the family Pannariaceae within the suborder Collematineae of the order Peltigerales. Phylogenetic analysis has shown that ''Leptogidium'' is sister to the genus ''Degelia'', specifically to ''Degelia gayana''.<ref name="Muggia et al. 2011"/>
==Description== ''Leptogidium'' is characterised by a distinctive thallus (lichen body) architecture and microscopic features. The thallus of ''Leptogidium'' species is radially symmetric and dendroid (tree-like) in structure, consisting of highly ramified, grey to dark brown branches. These branches are cylindrical ({{lichengloss|terete}}) and frequently divided, giving the lichen a minutely shrub-like or thread-like appearance. The thallus colour ranges from blue-grey to brown. This three-dimensional form is similar to that of ''Polychidium'', though it has evolved independently.
Microscopically, ''Leptogidium'' exhibits a distinctive arrangement of fungal cells around the {{lichengloss|photobiont}} (the photosynthetic partner in the lichen symbiosis). The fungal cells form a brickwork mosaic that envelops the cyanobacterial filaments, with the fungal cells shaped like interlocking puzzle pieces. This distinguishes ''Leptogidium'' from the related genus ''Polychidium'', where the cells are roundish. The outer layer ({{lichengloss|cortex}}) of the thallus is composed of tightly packed, angular fungal cells, forming a protective tissue called {{lichengloss|pseudoparenchyma}}.<ref name="Muggia et al. 2011"/><ref name="Cannon et al. 2021"/>
''Leptogidium'' species reproduce sexually through apothecia (disc-shaped fruiting bodies). The development of these fruiting bodies follows a hemiangiocarpic pattern, where the apothecia mature within thalline buds before emerging. When mature, the apothecia become exposed on the surface or slightly raised, appearing orange to red-brown in colour. They lack a {{lichengloss|thalline margin}} (an rim of tissue containing the lichen's photobiont) but possess a {{lichengloss|true exciple}} (an inner rim of fungal tissue). The photobiont associated with ''Leptogidium'' is the cyanobacterium ''Scytonema.''<ref name="Muggia et al. 2011"/><ref name="Cannon et al. 2021"/>
Inside the apothecia, ''Leptogidium'' produces spore-bearing sacs (asci), each containing eight colourless, ellipsoidal spores without internal divisions (septa). The asci are interspersed with sterile filaments called paraphyses, which have swollen tips. The genus also produces asexual reproductive structures (pycnidia), which are small, brown, and located on the sides of the branches. These produce tiny, rod-shaped reproductive cells called conidia.<ref name="Cannon et al. 2021"/>
Chemical analysis has not detected any lichen-specific substances in ''Leptogidium''.<ref name="Cannon et al. 2021"/>
==Species==
* ''Leptogidium byssoides'' {{au|(Carrington) Zahlbr. (1924)}} * ''Leptogidium contortum'' {{au|(Henssen) T.Sprib. & Muggia (2011)}} * ''Leptogidium dendriscum'' {{au|(Nyl.) Nyl. (1873)}} * ''Leptogidium intricatulum'' {{au|(Nyl.) Nyl. (1890)}} * ''Leptogidium neocaledonicum'' {{au|(Vain.) Zahlbr. (1924)}} * ''Leptogidium stipitatum'' {{au|(Vězda & W.A.Weber) T.Sprib. & Muggia (2011)}}
==References== {{Reflist|colwidth=30em|refs=
<ref name="Cannon et al. 2021">{{cite book |last1=Cannon |first1=P. |last2=Aptroot |first2=A. |last3=Coppins |first3=B. |last4=Sanderson |first4=N. |last5=Simkin |first5=J. |year=2021 |title=Peltigerales: Pannariaceae, including the genera ''Fuscopannaria'', ''Leptogidium'', ''Nevesia'', ''Pannaria'', ''Parmeliella'', ''Pectenia'', ''Protopannaria'' and ''Psoroma'' |series=Revisions of British and Irish Lichens |volume=9 |page=6 |url=https://britishlichensociety.org.uk/sites/default/files/Pannariaceae.pdf}}{{OA}}</ref>
<ref name="CoL">{{Catalogue of Life |id=5D35 |title=''Leptogidium'' |access-date=30 August 2024}}</ref>
<ref name="Muggia et al. 2011">{{cite journal |last1=Muggia |first1=Lucia |last2=Nelson |first2=Peter |last3=Wheeler |first3=Tim |last4=Yakovchenko |first4=Lidia S. |last5=Tønsberg |first5=Tor |last6=Spribille |first6=Toby |title=Convergent evolution of a symbiotic duet: The case of the lichen genus ''Polychidium'' (Peltigerales, Ascomycota) |journal=American Journal of Botany |volume=98 |issue=10 |year=2011 |doi=10.3732/ajb.1100046 |pmid=21980162 |pages=1647–1656 |url=https://www.researchgate.net/publication/51699827}}</ref>
<ref name="Nylander 1873">{{cite journal |last=Nylander |first=W. |year=1873 |title=Observata lichenologica in Pyrenaeis orientalibus. III. La Massane |journal=Flora (Regensburg) |volume=56 |pages=193–205 |language=la}}</ref>
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Category:Pannariaceae Category:Peltigerales genera Category:Lichen genera Category:Taxa described in 1873 Category:Taxa named by William Nylander (botanist)