I am an amateur naturalist trying to work out all the things living in my garden.
What better way than to start 2008 than with my second lichen (photo 1 - click to enlarge).
This one is growing on a bough of my garden apple tree (at (1.2,1.5) - see here) and is once again an example of a foliose (flakey, 'leaf like') lichen.
As explained in my previous posting, lichens are an organism that comprise a combination of a fungus and an algae. You might expect a curious life form such as this to have some unusual means of propagation and dispersal. In fact, lichens have at least three. The method(s) a given lichen favours can be a handy hint towards identification.
One method by which lichens disperse, as discussed last time, is via spores produced from fruit-like bodies called apothecia. The white bumps peppering my lichen's surface (thallus) in photo 1 are a second. As photo 2 (40x magnification) shows, these bumps consist of small white granules known as soredia. Soredia are little lumps of lichen (some fungal hyphae and a few algal cells) whose purpose is to flake away, hopefully to land somewhere new where they can set up home.
With regard to reaching a species identification, as I've said before I'm basically a novice when it comes to lichens. Based on the very handy A Key to Lichens on Twigs (Wolseley, James, Alexander) - a leaflet produced by the excellent Field Studies Council, together with a copy of the highly scholarly Lichens (F.S. Dobson, Richmond Publishing Co.) that Santa was generous to deliver me recently, I'm going with the identification Punctelia (Parmelia) subrudecta. I'm not 100% confident in this as the books above describe this species as having a grey thallus, whereas I'd definitely say that in my photo is greenish. That said however, the photo of P. subrudecta on the excellent site of the Botanical Museum of Oslo seems a good match. Furthermore, as I mentioned in my previous lichen posting, another handy tip for the identification of lichens is the use of chemical tests: according to the books, P. subrudecta turns red when exposed to a drop of sodium hypochlorite (=household bleach). The reaction was small and fleeting, but as shown in photo 3 (you'll want to click to enlarge), removing a small piece of my lichen and testing it resulted in just such a reaction. In short, I'll stick with identification for now and inmvite the experts out there to correct me!