Draft of Xanthoparmelia cumberlandia (Gyelnik) Hale for 2010/2011 EOL University Species Pages Initiative by Rachel Hawkins
Description status: Unreviewed
The Cumberland rock-shield (Xanthoparmelia cumberlandia) is a foliose, yellow-green lichen which is found across much of North and South America. It is a relatively large lichen and grows attached to rocks, where it is tightly attached and difficult to removed. Colonies of X. cumberlandia can be 3-12 cm across and are of varying shapes. The lobes of the lichen are divided into deep irregular shapes near the center and often have a black margin around the edges. The underside of the lichen is pale brown, with exposed strands of fungal hyphae known as rhizines.
Many brownish cup-shaped fruiting bodies, known as apothecia, are present on short stalks on the surface of the lichen. The apothecia are 2-10 mm in diameter and often have margins around the edges of the cup that are inrolled and “toothed.” Pycnidia, which are asexual reproductive organs, are also common on the lichen. Pycnidia are small, flask-shaped reproductive structures on the surface of the lichen body which produce microconidia, which produce single-nucleus cells as part of asexual reproduction. The pycnidia are very small and are visible as small black dots. There appears to be a reproductive threshold around the surface area of 10 cm^2. Below that area, there are usually no apothecia; above that area, almost all lichens possess apothecia. It also appears that older, sexual lichens devote more resources to reproduction than to growth, meaning they grow more slowly as they age.
Studies of the population structure of X. cumberlandia reveal that there are three distinct age classes: juvenile, adult, and senescent. Each class has a normal distribution with respect to size, so age is not necessarily correlated with size very strongly, especially if each class is the same age. The juvenile class tends to have the lowest mortality rate, and the senescent class tends to have the highest mortality rate. The population structure probably demonstrates that recruitment and establishment of new lichen colonies only happens occasionally, not annually. The Cumberland rock-shield is a poor colonizer; new colonies tend to be close nearby, and growth is only limited by other colonies, not competition from other species. The growth of the lichen is slowest in autumn and winter and highest in the summer months, perhaps because levels of precipitation drop during the colder months.
Diagnostic tests for lichens tend to be finicky and delicate; Xanthoparmelia cumberlandia is no exception. Crystal tests are often performed where certain acids are dissolved with bits of the thallus of the fungus, and then the residue is recrystallized and the color of the crystal is observed. The upper surface of the rock-shield reacts with PD+ to turn orange and with K+ to turn a yellow-orange. The same is true for the inner body of the lichen. X. cumberlandia does not react with C- when applied. The rock-shield also produces stictic, constictic, norstictic, usnic, and connorstictic acids as secondary compounds.
Morphologically, the Cumberland rock-shield is narrowly divided from its look-alikes and close relatives. The lower surface is pale. The lobes of the lichen are of varying shapes but are often divided into deep irregular segments, especially near the center. X. cumberlandia lacks asexual structures known as isidia, which are fingerlike, cylindrical growths from the upper outermost layer of the lichen body. It also lacks soredia, clumps of algal cells surrounded by fungal hyphae, which normally appear as a powdery substance on the lichen surface. These characters, along with chemical analysis, can allow the Cumberland rock-shield to be uniquely identified.
[Acids/substances used: C = sodium hypochloride; K = potassium hydroxide; KC = a combination of K and C; PD = paraphenylenediamine; UV = ultraviolet light.]
While X. cumberlandia was first described in the northeastern United States, it is widespread throughout North and South America. It has been found in the USA, Mexico, the Dominican Republic, Brazil, Uruguay, Venezuela, and the Cape Province of South Africa. There are two main swaths which cover the United States, with the exception of the central Great Plains. The Cumberland rock-shield grows slightly west of the Mississippi River, eastward to the Atlantic, and from northern Mississippi, Alabama, and Georgia northward to southern Canada. A western distribution of the rock-shield grows west of the Great Plains to the Pacific, avoiding most of Nevada and western Utah, and running from the Rio Grande in the south all the way to southern Canada. The presence of the lichen in South Africa seems unusual, given the widespread distribution in the Americas; it is possible that its presence there is human caused or initiated.
Xanthoparmelia cumberlandia prefers to grow upon partly submerged silicaceous rock. Boulders and smaller rocks close to the ground tend to be its main habitat. It can also be found at a variety of altitudes. Some studies have found X. cumberlandia growing upon siliceous granite gravestones; practically any silicaceous rock surface is suitable for X. cumberlandia to thrive.
The genus Xanthoparmelia is large, encompassing at least 400 species. There are several Xanthoparmelia species, some closely related to X. cumberlandia, which can easily be confused.
X. arseneana (Gyel.) Hale is found in the southwestern United States; it is either a variant of X. cumberlandia, or it intergrades very closely with it. However, X. arseneana has narrower lobes and hugs the rocks more tightly. X. ioannis-simae (Gyel.) Hale is also similar but has broader lobes with rounder tips; it also contains salazinic acid, while X. cumberlandia does not. X. angustiphylla is identical in chemistry and morphology to X. cumberlandia but has a black lower surface, while X. cumberlandia has a pale lower surface. X. plittii is identical except that it contains isidia, while X. cumberlandia does not. Finally, X. coloradoënsis is morphologically indistinguishable from X. cumberlandia. However, X. coloradoënsis produces salazinic, usnic, and perhaps consalazinic acids as secondary compounds, while X. cumberlandia produces stictic, constictic, norstictic, and usnic acids instead.
Xanthoparmelia cumberlandia has been shown to have active anti-herbivory compounds (like stictic acid) which have been shown to decrease herbivory in experiments with slugs, a major consumer of lichens. These lichens also have higher concentrations of N, P, and Ca, which are essential elements; as a result, they tend to produce more anti-herbivory compounds, possibly to discourage the leaching of essential elements. Other studies found that some of these these distasteful compounds also served as anti-microbial agents, effectively preventing bacteria and microbes from growing nearby. While these compounds have not been put to use yet, they have certainly been shown to be effective in controlling herbivory and microbial activity.
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Description author: Rachel Hawkins (Request Authorship Credit)
Created: 2010-12-12 15:21:09 EST (-0500) by Rachel Hawkins (rhawkins)
Last modified: 2010-12-12 15:35:48 EST (-0500) by Rachel Hawkins (rhawkins)
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