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Crustose Rock Lichens

Yaquina Head on the Oregon coast. Can you spot the zone of the marine lichen Verrucaria maura along the rocky shore?


Left: Lichen-covered gabbro boulder in the San Pasqual Valley of San Diego County, California. The lichen species include white (whitish-gray) Xanthoparmelia cumberlandia, yellowish-green Lecanora muralis and black Verrucaria (possibly V. viridula). Also on the boulder are small patches of red Caloplaca, yellow Candelariella, gray Aspicilia, and black Buellia. Right: Lichen-covered basalt boulder on the Santa Rosa Plateau of Riverside County, California. The lichen colonies form a dense crust of four colorful species, including red Caloplaca saxicola, yellow Candelaria concolor & Candelariella vitellina and gray Xanthoparmelia lineola.


Lichen-covered basalt boulder on the Santa Rosa Plateau of Riverside County, California. The lichen colonies form a dense crust of four colorful species, including red Caloplaca saxicola, yellow Candelaria concolor & Candelariella vitellina and gray Xanthoparmelia lineola.


Two of the most colorful crustose lichens in the Sierra Nevada of California. Left: Pleopsidium flavum. Note: Pleopsidium chlorophanum is a very similar species. Right: Caloplaca trachyphylla.


Rhizocarpon geographicum and Aspicilia cinerea? on Palomar Mountain.


Left: Lichen-covered granodiorite boulder in the hills northeast of Palomar College campus. The crustose lichen species include patches of white Dimelaena radiata and gray Aspicilia. The upper part of the rock is covered with black Buellia pullata. Right: Microscopic view (400x) of the apothecia of Buellia pullata showing brown, 2-celled (1-septate) spores, two spore-bearing asci (each with eight ascospores), and numerous clavate-tipped paraphyses. One ascus is mature and contains eight brown, 2-celled spores.

The Identification Of Buellia pullata


Left: Dimelaena thysanota and Right: D. oreina in the Sierra Nevada of California. Both of these crustose species have the characteristic marginally lobate thallus of this genus. They can be separated in the field by the color of their thallus. D. thysanota is brown, while the thallus of D. oreina is gray-green or greenish yellow, similar in color to Lecanora muralis, except the latter species has pinkish-tan apothecia.


Lichen-covered boulder in the Merriam Mountains of San Diego County, California. The lichen species include small patches of white Physcia albinea and larger patches of whitish-green (hale yellow) Xanthoparmelia mexicana. There are several other crustose species on this rock, including Dimelaena radiata, Buellia pullata and Aspicilia.


Lichen-covered boulder near June Lake in the Sierra Nevada of California. The lichen species include two species of Rhizoplaca, whitish R. chrysoleuca with flesh-colored apothecia and greenish R. melanophthera with dark gray apothecia. Other species on this rock include the brownish umbilicate lichen Umbilicaria phaea and black crustose Buellia.


Lichen-covered granite boulder near Devil's Post Pile National Monument in the Sierra Nevada of California. The two conspicuous lichen species are greenish Lecanora muralis and dark brown (blackish) Lecidea atrobrunnea.


Lecidea atrobrunnea growing on large, cubical crystal of feldspar in Cathedral Peak granite. Some of the major domes of Yosemite National Park are composed of this type of granite.


Colonies of lichens on alpine metamorphic outcrop above Gaylor Lakes in the Sierra Nevada. Some of the lichens include light gray foliose Umbilicaria, dark brown clumps of Acarospora thamnina, bright orange Caloplaca, yellow Candelariella, gray crustose Rhizocarpon disporum, dark brown crustose Staurothele clopima and Lecidea atrobrunnea.


Lichen-covered gabbro boulder on Palomar Mountain in San Diego County, California. The two white lichen colonies include two species of Lecanora: (A) Lecanora gangaleoides, an ashy-gray species with dark brown or tan apothecia; and (B) Possibly Lecanora rupicola, another ashy-gray species with numerous apothecia literally packed together and covered with white powder (pruinose). Also on the boulder is (C) Rhizocarpon geographicum, a common rock lichen in the Sierra Nevada, and several additional crustose species.


Close-up view of lichen-covered gabbro boulder on Palomar Mountain in San Diego County, California. The lichens in photo include two species of Lecanora. They both have apothecia with a thalline rim and colorless, oval spores (less than 20 micrometers in length and eight per ascus). Left: Lecanora rupicola, an ashy-gray areolate species with numerous apothecia literally packed together and covered with white powder (pruinose). The apothecia are K+ yellow and C+ yellow (using Clorox bleach). Right: Lecanora gangaleoides, an ashy-gray species with dark-brown or tan apothecia.


A vertical, metamorphic rock wall in the Sierra Nevada covered with colonies of lemon-yellow (chartreuse) Pleopsidium flavum and white Lecidea tessellata. Note: Pleopsidium chlorophanum is a very similar species. Lecidea tessellata is easily recognized by its cracked (areolate) grayish-white thallus and conspicuous black, convex apothecia.


A granite boulder in the Sierra Nevada of California covered by gray Rhizocarpon disporum, dark brown Staurothele clopima and lemon-yellow Candelariella. The ascus of R. disporum contains two brown, muriform spores (partitioned into sections like the squares of a Hershey's chocolate bar). Each spore is about 30 to 50 micrometers long. Staurothele is a pyrenocarpous lichen with sunken perithecia rather than apothecia. It resembles Verrucaria, except the spores of Staurothele are brown and muriform, while those of Verrucaria are simple (unpartitioned) and colorless.


Note: I originally thought the following images were Rhizocarpon disporum; however, the magnified view shows two spores per ascus and this species typically has one spore. Therefore, the microscope images are undoubtedly the closely related species R. geminatum.

Rhizocarpon geminatum (Previously labeled R. disporum) Left: Close-up view of lichen growing on a granitic outcrop in the Sierra Nevada of California. The thallus of this crustose lichen consists of numerous gray (tan), convex (bullate) areoles (similar to worts) scattered over a black hypothallus (prothallus) without algae. It superficially resembles light colored bumps on a black background. The black apothecium (red arrow) is similar to Lecidea without a thalline rim (i.e. without algal cells). Right: Microscopic view of an ascus (red arrow) containing two large muriform spores. Each spore is 30 to 50 micrometers long (1/500th of an inch). The brown spores are partitioned into smaller sections like the squares of a Hershey's chocolate bar.

See Muriform Spores Of A Crustose Soil Lichen


The animal enclosure walls at Horn and Hoof Mesa at the San Diego Zoo are colored lemon-yellow by the crustose lichen Caloplaca citrina. This is a calcium-loving lichen that grows well on concrete walls.

The animal enclosure walls at Horn and Hoof Mesa at the San Diego Zoo are colored lemon-yellow by the crustose lichen Caloplaca citrina. This is a calcium-loving lichen that thrives on concrete walls.

Lemon-yellow crustose lichen Caloplaca citrina growing on a tile roof.


Rock nipple lichen (Thelomma mammosum) in coastal San Diego County. Each nipple-like apotheciium is filled with a loose mass of black, single-celled spores called a mazaedium. In a mazaedium, the hymenial layer lining the inside of the apothecium has broken down and all the sac-like asci have released their spores. This explains why some of the apothecia are literally erupting with black spore masses.

Microscopic view of a mazaedium or spore mass from a nipple lichen (Thelomma mammosum). Right: High magnification showing the rough-walled spores. 1000x.

Rock nipple lichen (Thelomma mammosum) showing mass of black spores (mazaedium) extending out of a nipple-like apothecium.


Dimelaena radiata, a common gray, crustose lichen that grows on granitic boulders throughout the foothills of San Diego County. Although it superficially resembles other species of gray crustose rock lichens, it has characteristic 2-celled spores. The spores are produced 8 per ascus, and are brown at maturity.

Microscopic view of the transparent ascus of Dimelaena radiata containing eight 2-celled ascospores. The 2-celled spores are brown at maturity. They are approximately 10 to 12 micrometers in length.

Dimelaena radiata, a common gray, crustose lichen that grows on granitic boulders throughout the foothills of San Diego County. Although it superficially resembles other species of gray crustose rock lichens, it has brown 2-celled spores. In this photo several small colonies are growing on San Marcos gabbro, a dark, granitic rock

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