Biology Reference
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Figure 2: Some common cyanolichens. (A) Lobaria pulmonaria , on Acer saccharum . From the North Shore of Lake Superior,
Ontario. (B) Lobaria scrobiculata (damp), on Acer macrophyllum . From the central Coast Range of California. (C) Leptogium
cyanescens on mossy Acer saccharum bark. From Acadia National Park, Maine. (D) Peltigera aphthosa , on mossy soil. From
the Cascade foothills, western Oregon. Photographs courtesy Stephen Sharnoff, Missouri Botanical Garden, University of
California, Berkeley, CA, USA (http://www.sharnoffphotos.com/).
Color image of this figure appears in the color plate section at the end of the topic.
secondary lichen products a protective role has been assigned to these substances (Quilhot et al .,
1995, 2002; Holder et al ., 2000). We are presently at the threshold to understand these mechanisms
and whether these are specially adopted either by the mycobiont or the photobiont is the question
that has been addressed to during recent years. In the Antarctic epilithic lichen Xanthoria elegans , the
presence of parietin and β-carotene as the UV-protective compounds in upper cortex of mycobiont
has been demonstrated (Wynn-Williams, 2000). It is interesting to note that certain cyanobacteria
(Garcia-Pichel and Castenholz, 1993) produce mycosporine-like amino acids that act as intracellular,
cytoplasmic sunscreen pigments.
iii) Form of lichen thallus : The lichen thalli assume a variety of colours and shapes. They appear
greyish-green, white, orange, yellow, yellowish-green, brown or black. Traditionally, the lichens are
divided into three types based on the form of thallus. The fi rst type is crustose thallus which forms
a crust over the substratum. The second type is a foliaceous thallus which mostly resembles a leaf-
like structure and dried up thallus of a liverwort with lobed and irregular margins. The lichens that
assume a brush-like structure and are branched are included in the third type known as fruticose
lichens. These grow upright or pendant attached to bark of trees or rocks.
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