{{Short description|Species of lichen}} {{Use dmy dates|date=March 2023}} {{Speciesbox | image = | image_caption = | taxon = Heppia arenacea | authority = M.Schultz (2005) }}

'''''Heppia arenacea''''' is a species of terricolous (ground-dwelling) lichen in the family Lichinaceae.<ref name="CoL"/> Discovered in Yemen, it is characterized by its sand-coloured thallus and the incorporation of soil particles throughout its vegetative (i.e., non-reproductive) parts. The lichen is found in soil crust communities over limestone and basaltic rock in desert habitats, as well as in partially sheltered areas between large boulders.

==Taxonomy==

''Heppia arenacea'' was first formally described by German lichenologist Matthias Schultz in 2005. The type specimen was collected by the author in Wadi Asariah, Jabal Arays (Abyan Governorate) at an elevation of approximately {{convert|600|m|ft|abbr=on}}; there it was found growing on exposed soil over basaltic rock under an ''Anisotes trisulcus'' shrub.<ref name="Schultz 2005"/>

==Description==

''Heppia arenacea'' has a sand-coloured to pale ochre thallus, which can sometimes be slightly greyish-white {{lichengloss|pruinose}} and is somewhat gelatinous when wet. The thallus is {{lichengloss|squamulose}}, resembling an {{lichengloss|areolate}} crust with somewhat angular to roundish {{lichengloss|squamules}} measuring 0.6–2.5&nbsp;mm wide.<ref name="Schultz 2005"/>

Microscopically, the lichen's thallus anatomy is {{lichengloss|heteromerous}}, with an upper {{lichengloss|cortex}} 20–35&nbsp;μm thick, comprising {{lichengloss|paraplectenchymatous}} cells that are angulate to roundish and small, measuring 3–5&nbsp;μm wide. The {{lichengloss|photobiont layer}} is 75–150&nbsp;μm thick, consisting of vertical or irregular reticulate hyphae, with short to elongated cells measuring 7.5–12.5 by 2.5–3&nbsp;μm. The {{lichengloss|photobiont}} of ''Heppia arenacea'' is a filamentous cyanobacterium (''Scytonema''), present as short and contorted filaments or split individual cells. The filament cells are 7.5–12.5&nbsp;μm wide without a sheath and 10–17.5&nbsp;μm wide including the sheath. The lichen lacks a lower cortex and medulla. Except for the hymenium and {{lichengloss|subhymenium}}, abundant soil particles are incorporated in all parts of the thallus and apothecium.<ref name="Schultz 2005"/>

===Similar species===

''Heppia arenacea'' resembles ''Heppia despreauxii'', ''H.&nbsp;conchiloba'', and ''H.&nbsp;solorinoides'' in the presence of an {{lichengloss|epinecral layer}}, a distinct upper cortex, and the lack of a lower cortex. However, it is distinguished from other ''Heppia'' species by its unique sand-colored thallus and the incorporation of soil particles in its vegetative parts.<ref name="Schultz 2005"/>

==Habitat and distribution==

''Heppia arenacea'' is found in soil crust communities situated on limestone and basaltic rock in desert habitats. This lichen has been observed at elevations ranging from {{convert|200|to|2100|m|ft|abbr=on}} and has been recorded in a few distant regions in southern Yemen such as Djaul plateau, Ras Fartak, Jabal Arays, Wadi Raiwa, as well as on Socotra. The author suggests that the lichen may also be present in comparable habitats in Oman, Saudi Arabia, Eritrea, and Somalia. Typically, ''Heppia arenacea'' is found alongside free-living cyanobacteria (''Scytonema''), riccioid and marchantioid liverworts, and various soil lichens, including ''Collema coccophorum''., ''Psora decipiens'', ''Placidium'' spp., ''Toninia'' spp., ''Heppia'' spp., ''Peltula'' spp., and ''Gloeoheppia turgida''.<ref name="Schultz 2005"/>

==References== {{Reflist|refs=

<ref name="CoL">{{Catalogue of Life |id=3KWK7 |title=''Heppia arenacea'' M. Schultz |access-date=20 April 2023}}</ref>

<ref name="Schultz 2005">{{cite journal |last=Schultz |first=M. |title=''Heppia arenacea'' and ''Lempholemma polycarpum'', two new species from southern Yemen and Socotra |journal=The Lichenologist |volume=37 |issue=3 |year=2005 |doi=10.1017/s0024282905015161 |pages=227–235 |url=https://www.researchgate.net/publication/231982103}}</ref>

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{{Taxonbar|from=Q17387121}}

Category:Lichinomycetes Category:Lichen species Category:Lichens described in 2005 Category:Lichens of the Arabian Peninsula Category:Taxa named by Matthias Schultz