Name: Xanthoparmelia cumberlandia
Author: (Gyelnik) Hale
Deprecated Synonyms: Parmelia cumberlandia (Gyelnik) Hale
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.
Created: 2008-10-09 14:20:16 CST (+0800) by Jason Hollinger (jason)
Last modified: 2010-12-13 04:21:09 CST (+0800) by Rachel Hawkins (rhawkins)
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