This lunchtime I went along to Edinburgh's Royal Botanic Gardens for a guided walk round the garden's Lichen Safari Trail (I can't find reference to the lichen safari on the gardens own website, so the link above goes to Facebook).
It was a fascinating walk, checking out four of the stops on the trail
and spending time looking at the different lichens we saw there.
There are many species of lichen and some are notoriously difficult to tell apart but they are fascinating organisms, being a symbiosis between fungi and algae. There are three main types of lichens, the crustose (crusty) which are very tightly bound to the substrate like these ones on the stones in the Alpine Garden
and the foliose (leafy) like the one in the background in the centre of the photo above and also like the Xanthoria parietina below
Lichens can grow almost everywhere, the crusty lichens are best at growing in naturally harsh conditions. Lichens are very sensitive to air pollution and can be used to measure levels of pollution.
Edinburgh's Botanic Gardens are a great place to find lichens, you can buy a copy of the lichen safari booklet for £1 in the John Hope Gateway building. There's another walk next Thursday which I can definitely recommend going to if you're in Edinburgh.