{{Short description|Species of lichen}} {{Use dmy dates|date=January 2025}} {{Use British English|date=January 2025}} {{Speciesbox | image = The lichen Saxiloba firmula.png | image_caption = | taxon = Saxiloba firmula | authority = ([[Müll.Arg.]]) [[Robert Lücking|Lücking]], Moncada & [[Harrie Sipman|Sipman]] (2020) | synonyms_ref = <ref name="Species Fungorum synonymy"/> | synonyms = *''Porina firmula'' {{au|Müll.Arg. (1885)}} *''Verrucaria firmula'' {{au|(Müll.Arg.) [[Nyl.]] (1892)}}<ref name="Hue 1892"/> }}

'''''Saxiloba firmula''''' is a species of {{lichengloss|placodioid}} [[saxicolous lichen]] in the family [[Porinaceae]].<ref name="CoL"/> This lichen is native to the Caribbean, where it grows on [[calcareous]] rocks in shaded or semi-exposed habitats. Known for its distinctive [[rosette (botany)|rosette-like]] thallus with surface patterns, ''S.&nbsp;firmula'' exemplifies the [[morphology (biology)|morphological]] and ecological adaptations characteristic of the genus ''[[Saxiloba]]'', for which it is the [[type species]].

==Taxonomy==

''Saxiloba firmula'' was originally [[species description|described]] in 1872 by the Swiss lichenologist [[Johannes Müller Argoviensis]] as ''Porina firmula''.<ref name="Müller 1885"/> In 2020, [[Robert Lücking]], Bibiana Moncada, and [[Harrie Sipman]] transferred the species to the newly created genus ''[[Saxiloba]]'' based on its unique {{lichengloss|placodioid}} thallus [[morphology (biology)|morphology]] and [[molecular phylogenetics]] evidence. The genus was established to separate species with this morphology from other members of the family [[Porinaceae]].<ref name="Lücking et al. 2020"/>

==Description==

''Saxiloba firmula'' has a flattened, leaf-like [[thallus]] that forms tightly appressed [[rosette (botany)|rosettes]] measuring 10–20&nbsp;mm in diameter. The edges of the thallus feature distinct lobes, and its surface is marked by a network of fine, reticulate lines. These lines define chambers within the thallus that contain clusters of crystals, giving the lichen a textured appearance when wet. The colour of the thallus ranges from silvery grey-green to olive-grey.<ref name="Lücking et al. 2020"/>

The internal structure of ''S.&nbsp;firmula'' is complex, with a tightly packed fungal layer forming the upper cortex. Beneath this is the {{lichengloss|photobiont layer}}, which contains symbiotic [[green algae]] of the genus ''[[Trentepohlia (alga)|Trentepohlia]]''. Embedded within the photobiont layer are large crystal clusters, thought to play a role in light management. A loosely arranged [[medulla (lichenology)|medulla]] of fungal [[hypha]]e underlies the photobiont layer, and a dark {{lichengloss|hypothallus}} anchors the lichen to its rocky {{lichengloss|substrate}}.<ref name="Lücking et al. 2020"/>

Reproductive structures include [[perithecia]], which are immersed in the thallus and covered by a layer of fungal tissue. The reddish-brown to cherry-red [[ostiole]]s (openings) of the perithecia are visible on the surface. The [[ascus|asci]] within produce small, colourless, multi-septate {{lichengloss|ascospores}}.<ref name="Lücking et al. 2020"/>

==Habitat and distribution==

''Saxiloba firmula'' is found in the Caribbean, including Cuba, [[Isla de la Juventud]] (formerly Isle of Pines), [[Puerto Rico]], and the [[Bahamas]]. It primarily grows on [[calcareous]] rocks in dry forest habitats, favouring shaded or semi-shaded conditions. Despite its preference for shade, it can tolerate limited sun exposure, allowing it to inhabit a range of microhabitats.<ref name="Lücking et al. 2020"/>

The species' vertical arrangement of crystal clusters and algal cells within its thallus may enhance its ability to capture and utilise light in low-light environments. This adaptation likely contributes to its success in the often dim, shaded habitats it occupies.<ref name="Lücking et al. 2020"/>

==References== {{Reflist|refs=

<ref name="CoL">{{Catalogue of Life |id=B2N7K |title=''Saxiloba firmula'' (Müll. Arg.) Lücking, B. Moncada & Sipman |access-date=7 January 2025}}</ref>

<ref name="Hue 1892">{{cite journal |last=Hue |first=A. |year=1892 |title=Lichenes exoticos |journal=Nouvelles Archives du Museum d'Histoire Naturelle |volume=4 |pages=103–156}}</ref>

<ref name="Müller 1885">{{cite journal |last=Müller |first=J. |year=1885 |title=Pyrenocarpeae Cubenses a cl. C. Wright lectae |journal=Botanische Jahrbücher für Systematik, Pflanzengeschichte und Pflanzengeographie |volume=6 |pages=375–421 |language=la}}</ref>

<ref name="Lücking et al. 2020">{{cite journal |last1=Lücking |first1=Robert |last2=Moncada |first2=Bibiana |last3=Sipman |first3=Harrie |title=''Saxiloba'': a new genus of placodioid lichens from the Caribbean and Hawaii shakes up the Porinaceae tree (lichenized Ascomycota: Gyalectales) |journal=Plant and Fungal Systematics |volume=65 |issue=2 |year=2020 |doi=10.35535/pfsyst-2020-0031 |pages=577–585 |doi-access=free}}</ref>

<ref name="Species Fungorum synonymy">{{cite web |title=GSD Species Synonymy. Current Name: ''Saxiloba firmula'' (Müll. Arg.) Lücking, B. Moncada & Sipman, in Lücking, Moncada, Sipman, Sobreira, Viñas, Gutíerrez & Flynn, Plant and Fungal Systematics 65(2): 580 (2020) |url=https://www.speciesfungorum.org/GSD/GSDspecies.asp?RecordID=835481 |publisher=[[Species Fungorum]] |access-date=7 January 2025}}</ref>

}}

{{Taxonbar |from1=Q131704160 |from2=Q108282363}}

[[Category:Gyalectales]] [[Category:Lichen species]] [[Category:Lichens described in 1872]] [[Category:Lichens of the Caribbean]] [[Category:Taxa named by Johannes Müller Argoviensis]]