March 8, 2011:
Deciduous woodlands in Cumbria are the home to several species of lichen which are scarce elsewhere in England. Whilst searching for some of these yesterday, another more widespread lichen was seen and photographed. This was Peltigera praetextata Floerke ex Sommerf. which was growing on moss-covered boulders in woodland on the west side of Ullswater.
[Colour when dry; photo width = approx 10cm]
It is a relatively large 'leafy' lichen which anchors itself to the substrate by spike-like growths (rhizines) on its underside. The upper surface is brown to pale grey when dry but becomes dark grey or almost black when wet. The surface is bullate (i.e. it has raised vein) whilst the margins and surface cracks of older specimens can bear isidia (outgrowths containing its photosynthetic partner).
[Colour when wet. The isidia can be seen and also the bullate surface (in the lower part)]
This is the only relatively common British species of Peltigera which bears surface isidia. It is widespread and locally common on mossy boulders, tree-bases and on damp, heathy slopes.
[Showing the spike-like rhizines on the underside]