A lichen is a composite organism that arises from algae or cyanobacteria living among filaments of multiple fungi species in a mutualistic relationship. Lichens are important actors in nutrient cycling and act as producers which many higher trophic feeders feed on, such as reindeer, gastropods, nematodes, mites, and springtails. Lichens have properties different from those of their component organisms. They come in many colors, sizes, and forms and are sometimes plant-like, but are not plants. They may have tiny, leafless branches (fruticose); flat leaf-like structures (foliose); grow crust-like, adhering tightly to a surface (substrate) like a thick coat of paint (crustose); have a powder-like appearance (leprose); or other growth forms.
Flavoparmelia caperata, the common greenshield lichen, is a foliose lichen that grows on the bark of trees, and occasionally on rocks.
Flavoparmelia baltimorensis, the rock greenshield lichen, is a medium to large foliose lichen with a yellow green upper thallus surface when dry; its lobes are rounded without pseudocyphellae; and the upper surface is covered with globose, pustule-like growths resembling isidia. The lower surface is black with a narrow brown zone at the margins.
Parmelia sulcata is a foliose lichen in the family Parmeliaceae. It is very tolerant of pollution and has a cosmopolitan distribution, making it one of the most common lichens. It harbours a unicellular Trebouxia green algal symbiont.
Peltigerales is an order of lichen-forming fungi belonging to the class Lecanoromycetes in the division Ascomycota. The taxonomy of the group has seen numerous changes; it was formerly often treated as a suborder of the order Lecanorales. It contains two suborders, eight families and about 45 genera such as Lobaria and Peltigera.
The Stereocaulaceae are a family of lichen-forming fungi in the order Lecanorales. It contains five genera. Species of this family are widely distributed in temperate boreal and austral regions.
Lecanora is a genus of lichen commonly called rim lichens. Lichens in the genus Squamarina are also called rim lichens. Members of the genus have roughly circular fruiting discs (apothecia) with rims that have photosynthetic tissue similar to that of the nonfruiting part of the lichen body (thallus). Other lichens with apothecia having margins made of thallus-like tissue are called lecanorine.
Arthonia is a genus of lichens in the family Arthoniaceae. It was circumscribed by Swedish botanist Erik Acharius in 1806.
Flavoparmelia is a genus of foliose lichens in the family Parmeliaceae. Because of their appearance, they are commonly known as greenshield lichens. The widely distributed genus contains 32 species. It was circumscribed by American lichenologist Mason Hale in 1986 to contain 17 former Pseudoparmelia species with broad lobes, usnic acid in the cortex, and isolichenan in the cell walls.
Cetrelia is a genus of leafy lichens in the large family Parmeliaceae. They are commonly known as sea-storm lichens, alluding to the wavy appearance of their lobes. The name of the genus, circumscribed in 1968 by the husband and wife lichenologists William and Chicita Culberson, alludes to the former placement of these species in the genera Cetraria and Parmelia.
Parmotrema is a genus of lichen belonging to the family Parmeliaceae. It is a large genus, containing an estimated 300 species, with a centre of diversity in subtropical regions of South America and the Pacific Islands.
Xanthoparmelia is a genus of foliose lichen in the family Parmeliaceae. Xanthoparmelia is synonymous with Almbornia, Neofuscelia, Chondropsis, Namakwa, Paraparmelia, and Xanthomaculina. This genus of lichen is commonly found in the United States, as well as Australia, New Zealand and Ecuador.
Pseudocyphellae are structures in lichens that appear as tiny pores on the outer surface (the cortex of the lichen. They are caused when there is a break in the cortex of the lichen, and the medullary hyphae extend to the surface. Pseudocyphellae are the same colour as the medulla of the lichen, which is generally white, but can be yellow in some species of Pseudocyphellaria and in Bryoria fremontii. The presence/absence, abundance, colour, and shape of pseudocyphellae can all be diagnostic features used to identify different species. They facilitate gas exchange through the surface of the lichen, and may provide an adaptive advantage in temperate environments.
Lepraria is a genus of leprose crustose lichens that grows on its substrate like patches of granular, caked up, mealy dust grains. Members of the genus are commonly called dust lichens. The main vegetative body (thallus) is made of patches of soredia. There are no known mechanisms for sexual reproduction, yet members of the genus continue to speciate. Some species can form marginal lobes and appear squamulose. Because of the morphological simplicity of the thallus and the absence of sexual structures, the composition of lichen products are important characters to distinguish between similar species in Lepraria.
Chrysothrix is a genus of lichen-forming fungi in the family Chrysothricaceae. They are commonly called gold dust lichens or sulfur dust lichens, because they are bright yellow to greenish-yellow, sometimes flecked with orange, and composed entirely of powdery soredia. Apothecia are never present in North American specimens.
Lichens are symbiotic organisms made up of multiple species: a fungus, one or more photobionts and sometimes a yeast. They are regularly grouped by their external appearance – a characteristic known as their growth form. This form, which is based on the appearance of vegetative part of the lichen, varies depending on the species and the environmental conditions it faces. Those who study lichens (lichenologists) have described a dozen of these forms: areolate, byssoid, calicioid, cladoniform, crustose, filamentous, foliose, fruticose, gelatinous, leprose, placoidioid and squamulose. Traditionally, crustose (flat), foliose (leafy) and fruticose (shrubby) are considered to be the three main forms. In addition to these more formalised, traditional growth types, there are a handful of informal types named for their resemblance to the lichens of specific genera. These include alectorioid, catapyrenioid, cetrarioid, hypogymnioid, parmelioid and usneoid.
Punctelia graminicola is a species of foliose (leafy) lichen in the family Parmeliaceae. It grows on rocks, and, less frequently, on bark in North America, South America, and East Africa. It has a blue-grey thallus measuring up to about 15 cm (6 in), covered with tiny pores called pseudocyphellae. Sometimes the lichen forms small lobes that project out from the surface. Fruiting bodies are uncommon in this species; if present, they resemble small cups with a brown internal disc measuring 3–10 mm (0.1–0.4 in) in diameter. A lookalike species, Punctelia hypoleucites, is not readily distinguishable from Punctelia graminicola by appearance or habitat alone; these species can only be reliably differentiated by examining the length of their conidia.
The following outline provides an overview of and topical guide to lichens.
Gallowayella hasseana, the poplar sunburst lichen, is a species of corticolous (bark-dwelling), crustose lichen in the family Teloschistaceae. It occurs in North America.
