Friday, 22 March 2013

A rare lichen in Cumbria: Peltigera collina

February 26, 2013:
A rare forecast for good weather resulted in a hurriedly planned visit to the Seathwaite valley (Borrowdale, Cumbria) in the hope of finding and photographing Peltigera collina. In England this is a very scarce and local lichen and in Cumbria is restricted to growing on the trunks of a few ancient pollarded ash trees.

Peltigera collina (top two photos) and a pollarded ash (above) which had various other interesting and local lichens growing on the mossy lower part of its trunk. The marginal soredia can be seen in the centre photograph

In the beautiful warm summer-like weather P collina was soon located, low down near the base of just such a pollarded ash, although intermixed with three other species of Peltigera as well as Lobaria virens. Initially, this led to some confusion in identification but P. collina can be unequivocally distinguished from other British members of the genus in bearing clusters of soredia along the margins of its small neat upturned lobes. However even this was not completely straightforward because the neighbouring P. praetextata (see below) bore small isidia and folioles giving it a superficially similar appearance.

Peltigera praetextata, the marginal isidia and folioles can be seen in the lower photogrph

P. collina is a component of the 'Lobarion' association of lichens, a specific indicater and component of mild oceanic ancient woodlands. It occurs rather more frequently in north-west Scotland.

Peltigera horizontalis (sterile thallus)

Peltigera horizontalis

Lobaria virens

Seathwaite valley


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