NS3678 : A lichen - Parmelia saxatilis

near to Renton, West Dunbartonshire, Great Britain

A lichen - Parmelia saxatilis
A lichen - Parmelia saxatilis
This is an extremely common lichen in Britain. It can be found on moderately acidic bark as well as on rocks and walls.

(Compare a similar species: NS3678 : A lichen - Parmelia sulcata. Another species, P. ernstiae ( LinkExternal link ), is very similar to P. saxatilis, but is less common, and often has little lobules on its lobes.)

The example shown here was growing on one of the stones of a dry-stone wall.

On the upper surface, the outer layer (cortex) of the lobes is covered with a network of white lines; this network consists of pseudocyphellae (places where the cortex is thinner). Little stubby projections called isidia form on these lines; they are clearly visible through a lens, and, in this photograph, they give the centre of the lichen (which is densely covered with isidia) a rough appearance.

Isidia contain both fungal and algal cells (the two components of a lichen); they are designed to break off and propagate the lichen without the need for sexual reproduction. In some lichens, isidia are narrowed near the base so that they can break off more easily.

Parmelia saxatilis and P. sulcata are both assigned to zone 4 of the Hawksworth and Rose scale (see NS3778 : A lichen - Ramalina fastigiata), which means that they are fairly tolerant of sulphur dioxide pollution. However, they are much more vulnerable to other forms of air pollution: both of these species (as well as Hypogymnia physodes – NS3976 : A lichen - Hypogymnia physodes), "contain salazinic acid and seem to be especially sensitive to fluoride exposure" [Chapter 5 ("Fluorides") in "Pollution monitoring with lichens" by D.H.S.Richardson, 1992].

Historically, this species was used to produce a purple-brown dye. The lichen is sometimes said to have the common name Crottle, a name that is derived from the Gaelic "crotal"; however, both the Gaelic word and its English derivative can be broader in meaning. Under the headword "crotal", Dwelly's "Illustrated Gaelic-English Dictionary" gives the meaning: "general name for the varieties of lichen used for producing dyes of various shades of red and brown"; it also gives the more restricted meaning: "the lichen, stone- or heath-parmelia – Parmelia saxatilis and Parmelia omphalodes".
Creative Commons Licence [Some Rights Reserved]   © Copyright Lairich Rig and licensed for reuse under this Creative Commons Licence.
year taken
2009
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NS3678, 60 images   (more nearby)
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Image classification?
Supplemental image
Date Taken
Friday, 27 February, 2009   (more nearby)
Submitted
Sunday, 1 March, 2009
Geographical Context
Heath, Scrub 
Place (from Tags)
Carman Muir 
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Closeup  Life 
Category
Lichens and mosses   (more nearby)
Subject Location
OSGB36: geotagged! NS 3680 7848 [10m precision]
WGS84: 55:58.2896N 4:36.9990W
Photographer Location
OSGB36: geotagged! NS 3680 7848
View Direction
Southeast (about 135 degrees)
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