Flavoparmelia caperata, the common greenshield lichen, is a foliose lichen that grows on the bark of trees, and occasionally on rock.
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.
Caloplaca saxicola is a small bright orange crustose lichen that grows on rock all over the world. It is commonly called rock firedot lichen, jewel lichen or rock jewel lichen.
A foliose lichen is a lichen with flat, leaf-like lobes, which are generally not firmly bonded to the substrate on which it grows. It is one of the three most common growth forms of lichens. It typically has distinct upper and lower surfaces, each of which is usually covered with a cortex; some, however, lack a lower cortex. The photobiont layer lies just below the upper cortex. Where present, the lower cortex is usually dark, but occasionally white. Foliose lichens are attached to their substrate either by hyphae extending from the cortex or medulla, or by root-like structures called rhizines. The latter, which are found only in foliose lichens, come in a variety of shapes, the specifics of which can aid in species identification. Some foliose lichens attach only at a single stout peg called a holdfast, typically located near the lichen's centre. Lichens with this structure are called "umbilicate". In general, medium to large epiphytic foliose lichens are moderately sensitive to air pollution, while smaller or ground-dwelling foliose lichens are more tolerant. The term "foliose" derives from the Latin word foliosus, meaning "leafy".
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.
Acarospora socialis is a usually bright yellow areolate to squamulose crustose lichen in the family Acarosporaceae that grows up to 10 cm wide, mostly on rock in western North America. It is among the most common lichens in the deserts of Arizona and southern California. It grows on sandstone, intrusive and extrusive igneous rock such as granitics, in all kinds of exposures to sunlight, including vertical rock walls. It is found in North America, including areas of the Mojave Desert and Sonoran Desert region, to Baja California Sur. It is the most common yellow member of its genus in southwestern North America. It sometimes, but rarely, grows on other soil crusts. It is a pioneer species.
Collema nigrescens is a leafy (foliose) jelly lichen found growing on the bark of trees such as bigleaf maples, in wetter coastal parts of California. It is commonly called button jelly lichen or bat's wing lichen. It is blackish-green when wet, and dark brownish-green to dark olive when dry. The photosynthetic partner is the Nostoc cyanobacterium that is spread throughout the thallus. Although foliose in form, like all jelly lichens, the thallus is not differentiated, lacking layers or an upper or lower cortex (lichen) and the cyanobacteria is spread throughout the thallus. It has dark purple-brown apothecia all over. It produces no reaction to lichen spot tests.
Xanthoparmelia conspersa, commonly known as the peppered rock-shield, is a foliose lichen and the type species of genus Xanthoparmelia. It is widely distributed in temperate zones, and has been recorded from Japan, Europe, Africa, North America, and South America.
Xanthoparmelia maricopensis, the Maricopa rock-shield, is a 2–6 cm (0.8–2.4 in) wide, yellow-green foliose lichen in the Parmeliaceae family. It grows on igneous rock in southwestern North American deserts.
Circinaria arida is a 0.5–6 cm, light olive-brown custose lichen that grows on rock, often like a cluster of little light brown to olive balls growing on pebbles, in the southwestern deserts of North America. It is also found in Eurasia, and arid parts of North America from the southern Great Plains and Midwest to California. It is warty (verrucose) with the warts sometimes cracking apart areolate. The warts or areolas have angular to rounded sides. The 0.2-2.3 mm, convex to flat-topped areolas are separated by deep fissures that may be as deep (0.1–2 mm) as the areaola is wide, so the lichen often appears to be made of clusters of little balls crammed up next to each other, although the areolas are sometimes isolated. In California it is commonly found growing on pebbles. Each areola has a single sunken black, dust covered (pruinose) fruiting body (apothecium) with a white rim. A thin strip of prothallus sometimes is at the outer edge, forming a narrow dark zone (fimbriate). The similar Aspicilia desertorum has a white pruina on the apothecia. It is negative for lichen spot tests, I−, K−, P−, C−.
Oxneria fallax, also known as the hooded sunburst lichen, is a small yellow-orange to red-orange foliose lichen that grows on bark or rarely on rock or bone. It is found all over the world except very dry areas, with 10 species common in North America. The nonfruiting body (thallus) grows in rosettes to 3 cm in diameter. The rosettes sometimes coalesce with each other. The lobes may appear divided at the tips. It is sometimes tightly appressed to the substrate (adnate), and sometimes not. The fruiting bodies (apothecia) are lecanorine, meaning that they are disc-like with a ring or rim of tissue around the disc that is made of tissue similar to the thallus. The tips of the lobes form hood shaped soralia that produce powdery greenish yellow soredia. It prefers growing on elm or oak bark, but can also be found on rocks, bone, or other wood types. Lichen spot tests on the surface are K+ purple, C−, KC−, and P−.
Xanthoparmelia mexicana, commonly known as the salted rock-shield, is a foliose lichen in the family Parmeliaceae. It grows in 4–10 cm diameter rosettes of gray-green to yellow-green lobes in arid climates all over the world.
Rhizoplaca chrysoleuca is a pale yellowish-green to gray-green umbilicate foiliose lichen in the Lecanoraceae family. It was first described in 1791 by English botanist Sir James Edward Smith as Lichen chrysoleucus; Friedrich Wilhelm Zopf transferred it to the genus Rhizoplaca in 1905.
Heppia conchiloba is a gray to light brown squamulous to foliose terricolous lichen that occurs in southwestern deserts of North America. The surface appears as if covered in a light dust (pruinose). The squamules are peltate, up to 8 mm in diameter. There are one to several apothecia per lobe, with reddish-brown urn-shaped (urceolate) to concave discs, immersed so as to appear like concave spots. Lichen spot tests are all negative. Its entire thallus body is deeply convex, and it is different in color from other members of Heppia and or Peltula, which are olive or brownish-olive.
Acarospora strigata is an areolate to verruculous crustose lichen that grows on rock around the world, in full sun or shade, and in mesic to arid habitats. It is brown but may appear white or pale gray if it is covered in a pruina. The lichen is common in southwestern deserts of North America.
Lobothallia alphoplaca, the variable sunken disk lichen, is a creamy gray to brown, placodioid areolate lichen that grows on rock in on rock and sometimes moss. It prefers growing on siliceous rocks. It is found in Europe, central Asia, and North America, where it grows in the southwestern deserts to central California. The center has numerous crowded and deformed apothecia with rims of thallus-like tissue (lecanorine). With dark reddish or grayish brown to black discs. Lichen spot tests on the thallus and apothecia are C−, and KC−, with tests on the cortex K+ red, P+ orange, or K−, P− and on the medulla K+ red, and P+ orange. It produces norstictic acid, constictic acid, or salazinic acid as secondary metabolites.
Aspicilia californica is a small white to white mottled gray or gray-green foliose lichen, with stringy, terete, branch-like lobes. It is endemic to central and southern California, that grows on organic debris, moss, and rock in chaparral habitats. It attaches to the substrate at several points along the branch-like lobes. It may form areoles when growing on more solid substrates. Apothecia are rare. Lichen spot tests on the cortex and medulla are K+ red, KC-, C-, + orange, and I-. The olive brown Aspicilia filiformis is another fruticose species in this mostly crustose genus, occurring in Oregon, Idaho, Utah, Washington and Montana, with one known location also in California.
Buellia badia, the parasitic button lichen, is a dark chocolate-brown crustose areolate lichen of Europe, northern Africa, and North America that starts as a parasite growing on other lichens, such as Aspicilia phaea, gradually then becoming independent growing on rock (sometimes also on hardwood. Areoles may be contiguous or dispersed. Lecideine apothecia are 0.3 to 0.9 mm in diameter with black discs, that are initially flat, then become strongly convex as they age. Lichen spot tests are all negative. There are no known secondary metabolites as of. It is similar in appearance and other ways to the chocolate brown Dimelaena californica, which also starts off as a parasite on other lichens, and has spores of similar shape, size, and internal construction. D. californica has not been found on wood, is more preferential as to the lichens it starts growing on, and commonly has norstictic acid as a secondary metabolite. Some think they should be included in a new, third genus.
Physcia caesia, known colloquially as blue-gray rosette lichen and powder-back lichen, is a species of foliose lichenized fungus. First described by Georg Franz Hoffmann in 1784, it is common across much of Europe, North America and New Zealand, and more patchily distributed in South America, Asia, Australia and Antarctica. There are 2 subspecies: P. c. caesia and P. c. ventosa, as well as a number of distinct forms and varieties. Molecular studies suggest that the species as currently defined may be polyphyletic. It is typically pale gray shading to darker gray in the center, and grows in a small rosette, usually some 2–3 cm (0.79–1.18 in) across at maturity. It only rarely has apothecia, instead reproducing most often vegetatively via soredia, which are piled in round blue-gray mounds across the thallus's upper surface. It grows most often on rock—principally calcareous, but also basaltic and siliceous—and also occurs on bone, bark and soil. It is nitrophilic and is particularly common on substrates where birds perch.
Xanthoparmelia lineola, commonly known as the tight rock-shield, is a foliose lichen species in the genus Xanthoparmelia. It is a common species with a temperate distribution. Found in North America and South Africa, it grows on rocks.
