''Placidium'' 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
crustose
Crustose is a Habit (biology), habit of some types of algae and lichens in which the organism grows tightly appressed to a substrate, forming a biological layer. ''Crustose'' adheres very closely to the Substrate (biology), substrates at all poin ...
to
squamulose
A squamulose lichen is a lichen that is composed of small, often overlapping "scales" called . If they are raised from the substrate and appear leafy, the lichen may appear to be a foliose lichen, but the underside does not have a "skin" (cortex) ...
to almost
foliose
A foliose lichen is a lichen with flat, leaf-like , which are generally not firmly bonded to the substrate on which it grows. It is one of the three most common lichen growth forms, growth forms of lichens. It typically has distinct upper and lo ...
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 ...
s. The genus is in the family
Verrucariaceae
Verrucariaceae is a family of lichens and a few non-lichenised fungi in the order Verrucariales. The lichens have a wide variety of thallus forms, from crustose (crust-like) to foliose (bushy) and squamulose (scaly). Most of them grow on lan ...
.
Most members grow on soil (are
terricolous A terricolous lichen is a lichen that grows on the soil as a substrate. Examples include some members of the genus
Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classificati ...
), but some grow on rock (
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 ...
).
[ The fruiting bodies are ]perithecia
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. Ascoc ...
, flask-like structures immersed in the lichen body (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 ...
) with only the top opening visible, dotting the thallus. Lichen spot test
A spot test in lichenology is a spot analysis used to help identify lichens. It is performed by placing a drop of a chemical reagent on different parts of the lichen and noting the colour change (or lack thereof) associated with application of the ...
s are all negative. Members of the genus lack rhizines
In lichens, rhizines are multicellular root-like structures arising mainly from the lower surface. A lichen with rhizines is termed rhizinate, while a lichen lacking rhizines is termed erhizinate. Rhizines serve only to anchor the lichen to their s ...
, but otherwise resemble members of the genus '' Clavascidium''.[
Members of the genus are commonly called stiplescale lichens or earthscale.][Field Guide to California Lichens, Stephen Sharnoff, Yale University Press, 2014, ]
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 ...
in 1855 by Italian lichenologist Abramo Bartolommeo Massalongo
Abramo Bartolommeo Massalongo (13 May 1824 – 25 May 1860) was an Italian paleobotanist and lichenologist. He was born in Tregnago in the Province of Verona and took a great interest in botany as a young man. Massalongo joined the faculty of med ...
.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 ...
of genus ''Endocarpon
''Endocarpon'' is a genus of saxicolous (rock-dwelling), squamulose lichens in the family Verrucariaceae. It comprises 23 species.
Taxonomy
The genus was circumscribed by the German bryologist Johann Hedwig in 1789. '' Endocarpon pusillum'' was ...
'', '' E. pusillum''. When Othmar Breuss resurrected the genus for use in 1996,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 ...
.
Species
* '' Placidium arboreum''
* '' Placidium californicum''
References
{{Taxonbar, from=Q7200385
Verrucariales
Eurotiomycetes genera
Lichen genera
Taxa described in 1855
Taxa named by Abramo Bartolommeo Massalongo