{{Short description|Genus of lichens}} {{Use dmy dates|date=September 2024}} {{Use British English|date=September 2024}} {{Automatic taxobox | image = The lichen Saxiloba firmula.png | image_caption = ''Saxiloba firmula'' | taxon = Saxiloba | authority = [[Robert Lücking|Lücking]], Moncada & Viñas (2020) | type_species = ''Saxiloba firmula'' | type_species_authority = ([[Müll.Arg.]]) Lücking, Moncada & Sipman (2020) | subdivision_ranks = Species | subdivision = ''[[Saxiloba firmula|S. firmula]]''<br /> ''[[Saxiloba hawaiiensis|S. hawaiiensis]]''<br /> ''[[Saxiloba pruinosa|S. pruinosa]]'' }}
'''''Saxiloba''''' is a [[genus]] of [[lichen]]-forming [[fungi]] in the family [[Porinaceae]].<ref name="CoL"/> It comprises three species of [[saxicolous lichen|saxicolous]] (rock-dwelling) {{lichengloss|placodioid}} [[lichens]], known from [[disjunct distribution|disjunct]] locations in the Caribbean, Hawaii, and Brazil. The genus was [[circumscription (taxonomy)|circumscribed]] in 2020 to accommodate species with a distinctive {{lichengloss|placodioid}} thallus featuring unique surface patterns and internal crystal structures. ''Saxiloba'' lichens are characterised by their flattened, leaf-like thalli with marginal {{lichengloss|lobes}}, growing tightly appressed to rock surfaces. They have a complex internal structure, including large crystal clusters embedded within the {{lichengloss|photobiont layer}}, which may be an adaptation for light management in their typically shaded habitats.
==Taxonomy==
''Saxiloba'' was [[circumscription (taxonomy)|circumscribed]] in 2020 by [[Robert Lücking]], Bibiana Moncada, and Carlos Viñas to accommodate two species previously placed in other genera. The genus is characterised by its unique placodioid thallus with distinct marginal {{lichengloss|lobes}}, growing on rock with a {{lichengloss|trentepohlioid}} photobiont. It has a distinctive {{lichengloss|fenestrate}} thallus anatomy with conspicuous surface lines.<ref name="Lücking et al. 2020"/>
[[Molecular phylogenetics]] analysis places ''Saxiloba'' within the family [[Porinaceae]], but on a separate branch from other genera. Its position supports dividing Porinaceae into more genera than previously proposed. ''Saxiloba'' has a unique [[morphology (biology)|morphology]] and anatomy for Porinaceae, resembling some taxa in the related family [[Graphidaceae]].<ref name="Lücking et al. 2020"/> In a later analysis, it was shown by part of a [[lineage (evolution)|lineage]] with both [[saxicolous lichen|rock-dwelling]] and [[corticolous lichen|bark-dwelling]] ''Porina'' species having crustose and non-lobate thalli; as Damien Ertz and Paul Diederich suggest, "this raises some doubts about the use of the ascospores and thallus type alone for defining genera in the Porinaceae."<ref name="Ertz & Diederich 2022"/>
==Description==
''Saxiloba'' lichens are characterised by their distinctive {{lichengloss|placodioid}} thallus, meaning the lichen body forms a flattened, leaf-like structure with {{lichengloss|lobes}} around the edges. These lichens grow tightly appressed to rock surfaces, forming [[rosette (botany)|rosettes]] up to 10–20 mm in diameter. The thallus surface appears smooth but features a unique network of {{lichengloss|reticulate}} (net-like) or meandering lines, which are most visible when the lichen is wet. These lines surround chambers that contain clusters of crystals. The overall colour of the thallus varies between species, ranging from silvery grey-green to olive-yellow or yellowish grey-green.<ref name="Lücking et al. 2020"/>
In cross-section, the thallus reveals a complex structure. The upper layer ({{lichengloss|cortex}}) is composed of tightly packed fungal hyphae. Beneath this lies the {{lichengloss|photobiont layer}}, containing the algal partner (''[[Trentepohlia (alga)|Trentpohlia]]'') of the lichen symbiosis. Large, triangular to rhomboid clusters of crystals are embedded within the photobiont layer, giving the surface its distinctive patterned appearance. A [[medulla (lichenology)|medulla]] of loosely woven fungal [[hypha]]e sits below the photobiont layer. The bottom of the thallus features a dark brown to black {{lichengloss|hypothallus}}, which attaches the lichen to its rocky substrate.<ref name="Lücking et al. 2020"/>
The reproductive structures ({{lichengloss|perithecia}}) of ''Saxiloba'' are typically {{lichengloss|immersed}} in the thallus and covered by a layer of thallus tissue. The [[ostiole]] (opening) of the perithecium appears as a small, reddish-brown to cherry-red spot on the surface. Inside the perithecia, asci produce small, [[hyaline]] (colourless and transparent) {{lichengloss|ascospores}} with 3–5 cross-walls ([[septum|septa]]).<ref name="Lücking et al. 2020"/>
==Habitat and distribution==
''Saxiloba'' lichens are [[saxicolous lichen|saxicolous]], meaning they grow on rock surfaces. The genus has a [[disjunct distribution]] across [[tropical]] and [[subtropical]] regions, with species known from the Caribbean, Hawaii, and South America.<ref name="Lücking et al. 2020"/>
''[[Saxiloba firmula]]'', the type species, 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 forests of western and central Cuba, typically inhabiting shaded microhabitats, although it can tolerate some sun exposure.<ref name="Lücking et al. 2020"/>
''[[Saxiloba hawaiiensis]]'' is known only from its [[type locality (biology)|type locality]] on the island of [[Kauai]] in Hawaii. Unlike its Caribbean counterpart, this species grows on volcanic [[basalt]]. It was found in a disturbed forest habitat at an elevation of about 410 metres.<ref name="Lücking et al. 2020"/>
A third species, ''[[Saxiloba pruinosa]]'', was described in 2022 from Brazil. This species grows on half-exposed [[granite]] boulders in [[old-growth forest|primary]] rainforest in the state of [[Mato Grosso]], at elevations between 250 and 350 metres. It is currently only known from its type locality in the [[Reserva Cristalino]].<ref name="Aptroot et al. 2022"/>
The vertical arrangement of crystal clusters and algal cells within the thallus of ''Saxiloba'' species has been interpreted as an adaptation to manage light in their respective habitats. This structure could help distribute light more evenly through a thicker photobiont layer, potentially allowing the lichens to accumulate more [[biomass]] in low-light conditions.<ref name="Lücking et al. 2020"/>
==References== {{Reflist|refs=
<ref name="Aptroot et al. 2022">{{cite journal |last1=Aptroot |first1=André |last2=de Souza |first2=Maria Fernanda |last3=dos Santos |first3=Lidiane Alves |last4=Junior |first4=Isaias Oliveira |last5=Barbosa |first5=Bruno Micael Cardoso |last6=da Silva |first6=Marcela Eugenia Cáceres |title=New species of lichenized fungi from Brazil, with a record report of 492 species in a small area of the Amazon Forest |journal=The Bryologist |volume=125 |issue=3 |year=2022 |doi=10.1639/0007-2745-125.3.433 |pages=435–467}}</ref>
<ref name="CoL">{{Catalogue of Life |id=B2NWY |title=''Saxiloba'' |access-date=6 September 2024}}</ref>
<ref name="Ertz & Diederich 2022">{{cite journal |last1=Ertz |first1=Damien |last2=Diederich |first2=Paul |title=Unravelling the diversity of the lichen genus ''Porina'' (Porinaceae) in Mauritius |journal=Plant Ecology and Evolution |volume=155 |issue=1 |year=2022 |doi=10.5091/plecevo.84545 |pages=123–152|bibcode=2022PlEcE.155..123E |doi-access=free }}</ref>
<ref name="Lücking et al. 2020">{{cite journal |last1=Lücking |first1=Robert |last2=Moncada |first2=Bibiana |last3=Sipman |first3=Harrie |last4=Bezerra Sobreira |first4=Priscylla |last5=Viñas |first5=Carlos |last6=Gutíerrez |first6=Jorge |last7=Flynn |first7=Timothy |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>
}}
{{Taxonbar|from=Q130252077}}
[[Category:Gyalectales]] [[Category:Gyalectales genera]] [[Category:Taxa described in 2020]] [[Category:Taxa named by Robert Lücking]] [[Category:Lichen genera]] [[Category:Taxa named by Bibiana Moncada]]