''Racoleus'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial n ...

of two species of lichen-forming

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

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 hone ...

. Both species of ''Racoleus'' are

filamentous lichen Lichens are composite organisms made up of multiple species: a fungal partner, one or more photosynthetic partners, and sometimes a basidiomycete yeast. They are regularly grouped by their external appearance – a characteristic known as their ...

s with '' Trentepohlia'' (a genus of

green algae The green algae (singular: green alga) are a group consisting of the Prasinodermophyta and its unnamed sister which contains the Chlorophyta and Charophyta/ Streptophyta. The land plants ( Embryophytes) have emerged deep in the Charophyte alg ...

) as the partner. The lichens form

thalli Thallus (plural: 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. Many of these organisms wer ...

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, ...

Taxonomy

The genus was

circumscribed In geometry, the circumscribed circle or circumcircle of a polygon is a circle that passes through all the vertices of the polygon. The center of this circle is called the circumcenter and its radius is called the circumradius. Not every po ...

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, Swe ...

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 Museu ...

in 2011. The name ''Racoleus'' is derived by combining elements from two other genera: 'Rac' from '' Racodium'' and 'coleus' from ''

Cystocoleus ''Cystocoleus'' is a genus of lichen in the 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, in ...

''. 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 "unispec ...

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 Capnodiales. 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 Large S ...

, but DNA sequences of the

type species In 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 species that contains the biological type specimen( ...

, '' 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 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 ( ; ), sometimes termed an asexual chlamydospore or chlamydoconidium (), is an asexual, non-motile spore of a fungus. The word ''conidium'' comes from the Ancient Greek word for dust, ('). They are also called mitospores due to th ...

, 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. They are defined in latitude by the Tropic of Cancer in the Northern Hemisphere at N and the Tropic of Capricorn in the Southern Hemisphere at S. The tropics are also referred to ...

localities of '' Racoleus trichophorus'' – Africa (

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

), Asia (China), and South America (

Peru , image_flag = Flag of Peru.svg , image_coat = Escudo nacional del Perú.svg , other_symbol = Great Seal of the State , other_symbol_type = Seal (emblem), National seal , national_motto = "Fi ...

) – suggest that it could have a

pantropical A pantropical ("all tropics") distribution is one which covers tropical regions of both hemispheres. Examples of species include caecilians, modern sirenians and the plant genera ''Acacia'' and '' Bacopa''. '' Neotropical'' is a zoogeographic t ...

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 fungi in the family Pyrenulaceae. References External links *Pyrgillus' at Index Fungorum ''Index Fungorum'' is an international project to index all formal names (scientific names) in the fungus kingdom. the p ...

''), but is not considered to be

lichenicolous A lichenicolous fungus is a parasitic fungus that only lives on lichen as the host. A lichenicolous fungus is not the same as the fungus that is the component of the lichen, which is known as a lichenized fungus. They are most commonly specific t ...

(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, of the Holocene. It lasted from 3710 to 450 BCE. Etymology The composite scientific term ''Subboreal'', meaning "below the Boreal," is derived from the Latin ''sub'' (be ...

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

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