''Pleopsidium'' is a

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

lichen A lichen ( , ) is a hybrid colony (biology), colony of algae or cyanobacteria living symbiotically among hypha, filaments of multiple fungus species, along with yeasts and bacteria embedded in the cortex or "skin", in a mutualism (biology), m ...

-forming

fungi A fungus (: fungi , , , or ; or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and mold (fungus), molds, as well as the more familiar mushrooms. These organisms are classified as one ...

in the family

Acarosporaceae The Acarosporaceae are a family of fungi in the order Acarosporales. Members of this family have a widespread distribution, and are mostly lichenized with green algae. According to a 2021 estimate, the family contains 11 genera and about 260 spe ...

. The widespread genus, which contains four species, was

circumscribed In geometry, a circumscribed circle for a set of points is a circle passing through each of them. Such a circle is said to ''circumscribe'' the points or a polygon formed from them; such a polygon is said to be ''inscribed'' in the circle. * Circum ...

by lichenologist

Gustav Wilhelm Körber Gustav Wilhelm Körber (10 January 1817, Jelenia Góra, Hirschberg – 27 January 1885, Breslau) was a Silesian-German lichenologist and a professor at the University of Wrocław, University of Breslau. He specialized in the flora of Central Europ ...

in 1855.

Description

''Pleopsidium'' is a genus of

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 ...

s, typically forming small, patchy crusts divided into separate, block-like sections (). Around the edges, these lichens may develop elongated or somewhat shaped () lobes. The upper surface can be smooth or faintly wrinkled, and is most often a bright, vibrant yellow, though some specimens appear paler and slightly greenish. Beneath this surface layer, the

photosynthetic Photosynthesis ( ) is a Biological system, system of biological processes by which Photoautotrophism, photosynthetic organisms, such as most plants, algae, and cyanobacteria, convert light energy, typically from sunlight, into the chemical ener ...

partner is a

green alga The green algae (: green alga) are a group of chlorophyll-containing autotrophic eukaryotes consisting of the phylum Prasinodermophyta and its unnamed sister group that contains the Chlorophyta and Charophyta/ Streptophyta. The land plants ( ...

l cell type known as algae, arranged in a continuous layer. The upper —the thin protective "skin"” on top—is made of small, closely packed cells (), but there is no lower cortex on the underside. The reproductive structures, the

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

, sit either on the surface or are slightly embedded. Initially they are flat, gradually becoming more dome-shaped over time. These structures are often surrounded by a distinctive , especially in younger apothecia. The exposed centre () of the apothecium varies from yellow to brownish-yellow. Inside, numerous thin, branched, and

septate In biology, a septum (Latin for ''something that encloses''; septa) is a wall, dividing a cavity or structure into smaller ones. A cavity or structure divided in this way may be referred to as septate. Examples Human anatomy * Interatrial se ...

threads called help support the spore-producing tissue. The asci (spore sacs) are club-shaped, contain over a hundred spores each, and have a characteristic dome at their tip. They display a blue reaction when treated with a combination of

potassium Potassium is a chemical element; it has Symbol (chemistry), symbol K (from Neo-Latin ) and atomic number19. It is a silvery white metal that is soft enough to easily cut with a knife. Potassium metal reacts rapidly with atmospheric oxygen to ...

(K) and

iodine Iodine is a chemical element; it has symbol I and atomic number 53. The heaviest of the stable halogens, it exists at standard conditions as a semi-lustrous, non-metallic solid that melts to form a deep violet liquid at , and boils to a vi ...

(I) chemicals. The spores themselves are

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 ...

al, colourless, and do not have internal divisions. In addition to

sexual reproduction Sexual reproduction is a type of reproduction that involves a complex life cycle in which a gamete ( haploid reproductive cells, such as a sperm or egg cell) with a single set of chromosomes combines with another gamete to produce a zygote tha ...

through spores, ''Pleopsidium'' also reproduces via tiny, flask-shaped structures called

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 ...

, which are hidden within the thallus. These produce small, ellipsoidal

conidia A conidium ( ; : conidia), sometimes termed an asexual chlamydospore or chlamydoconidium (: chlamydoconidia), is an asexual, non- motile spore of a fungus. The word ''conidium'' comes from the Ancient Greek word for dust, ('). They are also ...

(asexual spores) that narrow slightly at one end. Chemically, ''Pleopsidium'' species contain

rhizocarpic acid Rhizocarpic acid is an organic compound with the molecular formula C28H23NO6 which has been isolated from the lichen ''Rhizocarpon geographicum'' and other lichens A lichen ( , ) is a hybrid colony (biology), colony of algae or cyanobacteri ...

as well as specific

fatty acid In chemistry, in particular in biochemistry, a fatty acid is a carboxylic acid with an aliphatic chain, which is either saturated and unsaturated compounds#Organic chemistry, saturated or unsaturated. Most naturally occurring fatty acids have an ...

s known as acaranoic and acarenoic acids. Ecologically, these lichens are typically found growing on rocks (

saxicolous 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 ...

) in cool and humid environments, where they can often be identified by their distinctive bright yellow crusts.

References

{{Taxonbar, from=Q7204599 Acarosporales Lecanoromycetes genera Lichen genera Taxa named by Gustav Wilhelm Körber Taxa described in 1855