''Racoleus'' 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 ...

of two species of

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 ...

of uncertain

familial Familial may refer to: * ''Familial'' (album), a 2010 studio album by Phil Selway *Family, a group of people affiliated by consanguinity, affinity, or co-residence *Family (biology), one of the eight major taxonomic ranks, classified between orde ...

placement in the order

Capnodiales Capnodiales is a diverse order of Dothideomycetes, initially based on the family Capnodiaceae, also known as sooty mold fungi. Sooty molds grow as epiphytes, forming masses of black cells on plant leaves and are often associated with the honeyd ...

. Both species of ''Racoleus'' are

filamentous lichen Lichens are symbiotic organisms made up of multiple species: a fungus, one or more photobionts (an alga and/or a cyanobacteria) and sometimes a yeast. They are regularly grouped by their external appearance – a characteristic known as their gro ...

s with '' Trentepohlia'' (a genus of

green algae 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 ...

) as the partner. The lichens form

thalli 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 ...

in the form of felt-like, blackish-brown cushions that grow under shaded conditions on

siliceous rock Siliceous rocks are sedimentary rocks that have silica (SiO2) as the principal constituent. The most common siliceous rock is chert; other types include diatomite. They commonly form from silica-secreting organisms such as radiolarians, diatoms, o ...

Taxonomy

The genus 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 the lichenologists

Rolf Santesson Rolf Santesson (1916–2013) was a Swedish lichenologist and university lecturer. He was awarded the Acharius Medal in 1992 for his lifetime contributions to lichenology. Early life and education Santesson was born in 1916 in Trollhättan, Sw ...

and

David Leslie Hawksworth David Leslie Hawksworth (born 1946 in Sheffield, UK) is a British mycologist and lichenologist currently with a professorship in the Universidad Complutense de Madrid in Madrid, Spain and also a Scientific Associate of The Natural History Mu ...

in 2011. The name ''Racoleus'' is derived by combining elements from two other genera: 'Rac' from '' Racodium'' and 'coleus' from '' Cystocoleus''. This naming reflects the genus's shared characteristics with both ''Racodium'' and ''Cystocoleus'', which are also filamentous lichens. The authors placed the genus in the order

because of morphological characteristics. ''Racoleus'' was

monotypic In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unisp ...

until 2023, when a second species was added to the genus.

Molecular phylogenetic Molecular phylogenetics () is the branch of phylogeny that analyzes genetic, hereditary molecular differences, predominantly in DNA sequences, to gain information on an organism's evolutionary relationships. From these analyses, it is possible to ...

analysis suggests that the new species belongs to the family

Teratosphaeriaceae Teratosphaeriaceae is a family of fungi in the order Mycosphaerellales. History In 2007, this family was recognized as distinct from the genus ''Mycosphaerella'', where it had previously been located, based on phylogenies constructed with the ...

, but DNA sequences of the

type species In International_Code_of_Zoological_Nomenclature, zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the spe ...

, '' R. trichophorus'', were not available for analysis.

Description

''Racoleus'' is characterised by a superficial, fluffy, and filamentous thallus, which typically presents a brown colour. This genus has a unique relationship with its photobiont, '' Trentepohlia'', a type of

. In this

symbiotic Symbiosis (Ancient Greek : living with, companionship < : together; and ''bíōsis'': living) is any type of a close and long-term biolo ...

relationship, individual ''Trentepohlia'' filaments are completely encased by fungal

hypha A hypha (; ) is a long, branching, filamentous structure of a fungus, oomycete, or actinobacterium. In most fungi, hyphae are the main mode of vegetative growth, and are collectively called a mycelium. Structure A hypha consists of one o ...

e, which are the filament-like structures of the fungus. The structure of ''Racoleus'' is complex, with its filaments ranging from slightly upright (suberect) to spreading out across the surface (decumbent or spreading). These filaments have a branching pattern known as sympodial, where new growth emerges from the side of an older growth. The outer walls of these filaments are distinctive, with an undulating and irregularly corrugated texture, adorned with numerous spiny projections. The fungal hyphae that envelop the algal filament form a single layer. These hyphae are oriented vertically and run parallel to the axis of the algal filament. They are brown in colour and are marked by thick, uneven walls that are corrugated but not ornamented. The spines that emerge from these filaments are notable for their stiffness, thickness, and smooth, unadorned surfaces. They protrude at angles ranging from broadly acute to almost right angles relative to the vertical axis of the filament. As for reproductive structures, specific details about the conidiogenous cells (cells that produce

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 ...

, a type of asexual fungal spore) and the conidia themselves are not well established or known for ''Racoleus''.

Habitat and distribution

The reported

tropical The tropics are the regions of Earth surrounding the equator, where the sun may shine directly overhead. This contrasts with the temperate or polar regions of Earth, where the Sun can never be directly overhead. This is because of Earth's ax ...

localities of '' Racoleus trichophorus'' – Africa (

Ivory Coast Ivory Coast, also known as Côte d'Ivoire and officially the Republic of Côte d'Ivoire, is a country on the southern coast of West Africa. Its capital city of Yamoussoukro is located in the centre of the country, while its largest List of ci ...

), Asia (China), and South America (

Peru Peru, officially the Republic of Peru, is a country in western South America. It is bordered in the north by Ecuador and Colombia, in the east by Brazil, in the southeast by Bolivia, in the south by Chile, and in the south and west by the Pac ...

) – suggest that it could have a

pantropical A pantropical ("all tropics") distribution is one which covers tropical regions of both the Eastern and Western hemispheres. Examples of species include caecilians, modern sirenians and the plant genera ''Acacia'' and ''Bacopa''. ''Neotropical' ...

distribution. It is often found growing on the thalli of whitish crustose lichens (including '' Dichosporidium brunnthaleri'', '' D. nigrocinctum'', and ''

Pyrgillus indicus ''Pyrgillus'' is a genus of lichen-forming fungi in the family Pyrenulaceae. The genus was circumscribed by the Finnish lichenologist William Nylander in 1858. Species * '' Pyrgillus americanus'' * '' Pyrgillus aurantiacus'' * '' Pyrgillus cam ...

''), but is not considered to be

lichenicolous 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 ...

(lichen-dwelling), as the contact between them seems to be superficial. ''Racoleus japonicus'' occurs in

subboreal The Subboreal is a climatic period, immediately before the present one, the subatlantic period. Both are part of the Holocene epoch. It lasted from 3710 to 450 BCE. During this time, conditions on earth were somewhat warmer and drier than the p ...

temperate In geography, the temperate climates of Earth occur in the middle latitudes (approximately 23.5° to 66.5° N/S of the Equator), which span between the tropics and the polar regions of Earth. These zones generally have wider temperature ran ...

regions of Japan, where it grows on shaded rocks and rock walls.

References

{{Taxonbar, from=Q107279828 Capnodiales Dothideomycetes genera Taxa described in 2011 Lichen genera Taxa named by David Leslie Hawksworth Taxa named by Rolf Santesson