Species of the Month - January 2019

Common Dog Lichen

Peltigera membranacea

Peltigera membranacea is the commonest of the dog lichens, and for many people it's the first lichen they notice and learn to recognise.  However there are several other species of dog lichen and this page tells you how to be sure you have the Common Dog Lichen.  You will then begin to notice other kinds of dog lichen too.
 

The upper surface is wrinkled, with low elongated raised areas and narrow channels between them.  This kind of wrinkling is called "bullate".  There is a fine coating of down on the surface, as the above left photo shows.  Sometimes this will have rubbed off in places, but you can generally find some on the younger parts of the lichen, at the lobe ends, away from the centre.

The photo on the right above shows the reddish-brown fruitbodies, which are sometimes abundant, but may be completely absent.
 

The underside shows the "fangs" that give it the name Dog Lichen.  It was once thought to be a cure for rabies because of this feature.  The fangs are rhizines, which anchor the lichen to the surface it's growing on.  In Common Dog Lichen, these each arise from an independent base, and are unbranched, but covered with short hairs which spread out to some extent, or can be matted together in wet material.  The protruding hairs are similar in length to the width of the rhizine, and can give a bottle-brush effect.

There are 2 other dog lichens that have a downy and bullate upper surface, but they differ from P membranacea in their rhizines.

P canina has branched bushy rhizines that are joined together at the base, with little or no gap between one and the next.  It is uncommon.

P praetextata has rhizines that are very smooth, with any hairs sticking out being minute in length, much less than the width of the rhizine.  It also nearly always has clusters of small scales along the margins and along cracks in the upper surface.  It is fairly common in our area, mostly on trees, sometimes on shady rocks.

Young specimens of P membranacea might be confused with these other species, but it is nearly always easy to find large extensive patches of mature P membranacea, so it is best to ignore smaller pieces that you're not sure of.
 

Common Dog Lichen loves growing over moss, whether the moss is on stones, trees, or on the ground.  It thrives in places that are somewhat shaded and damp.  The one on the left above is on a dry stone wall overhung by trees.  On the right is one growing on a hazel tree.  This one still has most of its downy covering, but this has worn off in places leaving the exposed surface looking darker than where the down is still in place.
 

Common Dog Lichen can occasionally be the dominant lichen on a tree and rampages all over it.  This photo by Jan Hamilton, from the 2014 LNHG field trip at Cologin, shows it wrapping itself round the broken base of a dead willow branch.

Another photo by Jan, from the slopes of Meall Mor, a mature patch with lots of fruit but only small amounts of down left on the surface.

Please send in your Common Dog Lichen sightings using the form below, or email sightings@lnhg.org.uk with the details if you prefer.  If you are not sure of the identity of your lichen, please send a photo to sightings@lnhg.org.uk, or put one on the LNHG Facebook page.