''Astrothelium xanthosordithecium'' is a species of

corticolous This glossary of mycology is a list of definitions of terms and concepts relevant to mycology, the study of fungi. Terms in common with other fields, if repeated here, generally focus on their mycology-specific meaning. Related terms can be found ...

(bark-dwelling,

crustose lichen Crustose lichens are lichens that form a crust which strongly adheres to the Substrate (biology), substrate (soil, rock, tree bark, etc.), making separation from the substrate impossible without destruction. The basic structure of crustose lichen ...

in the family

Trypetheliaceae The Trypetheliaceae are a family of mainly lichen-forming fungi in the order Trypetheliales. The family consists almost exclusively of corticolous (bark-dwelling), crustose lichens with an almost strictly tropical distribution. Taxonomy Trypethe ...

. The lichen grows in the rainforests of

Minas Gerais Minas Gerais () is one of the 27 federative units of Brazil, being the fourth largest state by area and the second largest in number of inhabitants with a population of 20,539,989 according to the 2022 Brazilian census, 2022 census. Located in ...

, Brazil. It contains the chemical

lichexanthone Lichexanthone is an organic compound in the structural class of chemicals known as xanthones. Lichexanthone was first isolated and identified by Japanese chemists from a species of foliose lichen, leafy lichen in the 1940s. The compound is known ...

, a

secondary metabolite Secondary metabolites, also called ''specialised metabolites'', ''secondary products'', or ''natural products'', are organic compounds produced by any lifeform, e.g. bacteria, archaea, fungi, animals, or plants, which are not directly involved ...

that causes it to

fluoresce Fluorescence is one of two kinds of photoluminescence, the emission of light by a substance that has absorbed light or other electromagnetic radiation. When exposed to ultraviolet radiation, many substances will glow (fluoresce) with color ...

when lit with an

ultraviolet Ultraviolet radiation, also known as simply UV, is electromagnetic radiation of wavelengths of 10–400 nanometers, shorter than that of visible light, but longer than X-rays. UV radiation is present in sunlight and constitutes about 10% of ...

light.

Taxonomy

The Dutch lichenologist

André Aptroot André Aptroot ( Heemskerk, 1961) is a Dutch mycologist and lichenologist. His primary research focus is on biodiversity, particularly tropical lichens, encompassing systematics, floristic surveys, and taxonomic reviews. A prolific research ...

formally described ''Astrothelium xanthosordithecium'' in 2022, highlighting its unique chemical composition compared to its closest relative, '' Astrothelium sordithecium''. The

species epithet Specific name may refer to: * in Database management systems, a system-assigned name that is unique within a particular database In Taxonomy (biology), taxonomy, either of these two meanings, each with its own set of rules: * Specific name (botany) ...

''xanthosordithecium'' alludes to its distinctive feature: the presence of

, a yellow pigment, contrasting with the brownish (a tissue in the ascomata containing

spore In biology, a spore is a unit of sexual reproduction, sexual (in fungi) or asexual reproduction that may be adapted for biological dispersal, dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores fo ...

-producing cells) of ''A. sordithecium''. The

type specimen In biology, a type is a particular wikt:en:specimen, specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally associated. In other words, a type is an example that serves to ancho ...

was collected from the Santuário do Caraça in

, at an elevation between .

Description

The

thallus Thallus (: thalli), from Latinized Greek (), meaning "a green shoot" or "twig", is the vegetative tissue of some organisms in diverse groups such as algae, fungi, some liverworts, lichens, and the Myxogastria. A thallus usually names the entir ...

of ''Astrothelium xanthosordithecium'' is slightly shiny and olivaceous green, spreading up to in diameter and about 0.1 mm thick. It closely follows the without forming a

prothallus A prothallus, or prothallium, (from Latin ''pro'' = forwards and Greek ''θαλλος'' (''thallos'') = twig) is usually the gametophyte stage in the life of a fern or other pteridophyte. Occasionally the term is also used to describe the young ...

, an initial growth phase or border seen in other lichens. Reproductive structures (

ascomata An ascocarp, or ascoma (: ascomata), is the fruiting body (sporocarp (fungi), sporocarp) of an ascomycete phylum fungus. It consists of very tightly interwoven hyphae and millions of embedded ascus, asci, each of which typically contains four to ...

) are pear-shaped and fused, forming within , a tissue structure that houses multiple ascomata. These pseudostromata are often whitish, round to lobate, and can be 1–3 mm in diameter and 0.9–1.4 mm high. Each pseudostromatum typically has a single group of fused ascomata, thus a single

ostiole An ''ostiole'' is a small hole or opening through which algae or fungi release their mature spores. The word is a diminutive of wikt:ostium, "ostium", "opening". The term is also used in higher plants, for example to denote the opening of the ...

(opening), which is black and eccentric (off-centre). The internal tissue, or hamathecium, contains tiny brownish oil globules. The lichen produces eight spores per

ascus An ascus (; : asci) is the sexual spore-bearing cell produced in ascomycete fungi. Each ascus usually contains eight ascospores (or octad), produced by meiosis followed, in most species, by a mitotic cell division. However, asci in some gen ...

, which are clear (

hyaline A hyaline substance is one with a glassy appearance. The word is derived from , and . Histopathology Hyaline cartilage is named after its glassy appearance on fresh gross pathology. On light microscopy of H&E stained slides, the extracellula ...

), dividided into four compartments by

septa SEPTA, the Southeastern Pennsylvania Transportation Authority, is a regional public transportation authority that operates bus, rapid transit, commuter rail, light rail, and electric trolleybus services for nearly four million people througho ...

(3-septate), and measure 34–37 by 10–12

μm The micrometre (Commonwealth English as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American English), also commonly known by the non-SI term micron, is a unit of length in the International System ...

. These spores are long-

ellipsoid An ellipsoid is a surface that can be obtained from a sphere by deforming it by means of directional Scaling (geometry), scalings, or more generally, of an affine transformation. An ellipsoid is a quadric surface; that is, a Surface (mathemat ...

in shape and do not have a surrounding gelatinous sheath. No

pycnidia A pycnidium (plural pycnidia) is an asexual fruiting body produced by mitosporic fungi, for instance in the order Sphaeropsidales ( Deuteromycota, Coelomycetes) or order Pleosporales (Ascomycota, Dothideomycetes). It is often spherical or inve ...

(structures for

asexual reproduction Asexual reproduction is a type of reproduction that does not involve the fusion of gametes or change in the number of chromosomes. The offspring that arise by asexual reproduction from either unicellular or multicellular organisms inherit the f ...

) were observed. Chemically, both the thallus and pseudostromata show a yellow

fluorescence Fluorescence is one of two kinds of photoluminescence, the emission of light by a substance that has absorbed light or other electromagnetic radiation. When exposed to ultraviolet radiation, many substances will glow (fluoresce) with colore ...

under

light.

Thin-layer chromatography Thin-layer chromatography (TLC) is a chromatography technique that separates components in non-volatile mixtures. It is performed on a TLC plate made up of a non-reactive solid coated with a thin layer of adsorbent material. This is called the sta ...

confirmed the presence of lichexanthone, a

that contributes to the lichen's unique characteristics.

Similar species

''Astrothelium xanthosordithecium'' is closely related to ''Astrothelium sordithecium'', sharing the habitat and the brownish hamathecium inspersion. However, it is distinguishable by its chemical composition, specifically the presence of lichexanthone, which sets it apart from any other species within ''Astrothelium''.

References

{{Taxonbar, from=Q131644838 xanthosordithecium Lichen species Lichens described in 2022 Lichens of Brazil Taxa named by André Aptroot