{{Short description|Species of lichen}} {{Use dmy dates|date=February 2024}} {{Speciesbox | image = Pyxine petricola - Flickr - pellaea.jpg | image_caption = | status = G4 | status_system = TNC | status_ref = <ref name=NS>{{cite NatureServe |id=2.122872 |title=''Pyxine petricola'' |access-date=5 November 2025}}</ref> | taxon = Pyxine petricola | authority = [[Nyl.]] (1876) | synonyms_ref = <ref name="Species Fungorum synonymy"/> | synonyms = *''Pyxine meissneri'' var. ''endoleuca'' {{au|[[Müll.Arg.]] (1879)}} *''Pyxine endoleuca'' {{au|(Müll.Arg.) [[Vain.]] (1898)}} *''Pyxine subvelata'' {{au|[[Stirt.]] (1898)}} }}

'''''Pyxine petricola''''' is a species of [[saxicolous lichen|saxicolous]] (rock-dwelling), [[foliose lichen]] in the family [[Caliciaceae]].<ref name="CoL"/> The distribution of the lichen includes Australia, East Africa, North and Central America, and the Philippines.<ref name="Rogers 1986"/>

==Taxonomy==

The lichen was [[species description|formally described]] as a new species in 1876 by the Finish lichenologist [[William Nylander (botanist)|William Nylander]]. In Nylander's brief description, he mentions that ''Pyxine petricola'' has a slightly blue-green [[thallus]], spreading thinly and attaching closely to surfaces. Its reproductive structures, [[apothecia]], are black, flat, and edged, with dark, oblong, two-compartment spores. The top cell layer of the apothecium is bluish-black, contrasting with the nearly colourless layer beneath. He further notes that the species typically grows on rocks.<ref name="Crombie 1876"/>

==Description== The [[thallus]] of ''Pyxine petricola'', the lichen typically does not exceed a diameter of {{cvt|40|mm}} and features a thallus with irregular or radially arranged {{lichengloss|lobes}}. These lobes, measuring between 0.3 and 1.2&nbsp;mm in width, are white or greyish white in colour and have a branching pattern that is somewhat {{lichengloss|dichotomous}} (splitting into two parts) and often overlapping ({{lichengloss|imbricate}}), lying flat against or slightly raised from the surface. The thallus may be smooth or slightly convex, with [[pseudocyphella]]e—specialised pores allowing [[gas exchange]]—visible as white lines along the margins and upper surface, sometimes forming a network ({{lichengloss|reticulate}}). Unlike some lichens, ''Pyxine petricola'' does not develop [[isidia]] (outgrowths for reproduction and dispersal) or {{lichengloss|pustules}}, and may or may not be covered in a fine powder ({{lichengloss|pruina}}). The inner tissue ([[medulla (lichenology)|medulla]]) of the lichen is white.<ref name="Rogers 1986"/>

Reproductive structures ([[apothecia]]) are commonly found within the lichen, often incorporating algae within their outer rim ({{lichengloss|exciple}}) and featuring an internal structure (stipe) that turns red when treated with a [[potassium hydroxide]] solution (i.e., the K [[spot test (lichen)|spot test]]). The {{lichengloss|ascospores}} measure 12–20 by 6–8&nbsp;[[μm]].<ref name="Rogers 1986"/>

Chemically, ''Pyxine petricola'' is distinguished by the presence of [[lichexanthone]] and [[triterpene]]s. The outer layer (cortex) of the lichen [[fluoresce]]s yellow under [[ultraviolet light]] but is K− and Pd−.<ref name="Rogers 1986"/>

==References== {{Reflist|refs=

<ref name="CoL">{{Catalogue of Life |id=7928R |title=''Pyxine petricola'' Nyl. |access-date=24 February 2024}}</ref>

<ref name="Crombie 1876">{{cite journal |last=Crombie |first=J.M. |year=1876 |title=New Lichens from the Island of Rodriguez |journal=Journal of Botany, British and Foreign |volume=14 |pages=262–265 |url=https://www.biodiversitylibrary.org/page/9103457}}</ref>

<ref name="Rogers 1986">{{cite journal |last=Rogers |first=R.W. |year=1986 |title=The genus ''Pyxine'' (Physciaceae, lichenized ascomycetes) in Australia |journal=Australian Journal of Botany |volume=34 |issue=2 |pages=131–154 |doi=10.1071/BT9860131}}</ref>

<ref name="Species Fungorum synonymy">{{cite web |title=GSD Species Synonymy. Current Name: ''Pyxine petricola'' Nyl., in Crombie, J. Bot., Lond. 14: 263 (1876) |url=https://www.speciesfungorum.org/GSD/GSDspecies.asp?RecordID=355845 |publisher=[[Species Fungorum]] |access-date=24 February 2024}}</ref>

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[[Category:Pyxine|petricola]] [[Category:Lichen species]] [[Category:Lichens described in 1876]] [[Category:Lichens of Africa]] [[Category:Lichens of Australia]] [[Category:Lichens of Central America]] [[Category:Lichens of Malesia]] [[Category:Lichens of North America]] [[Category:Taxa named by William Nylander (botanist)]]