A closer look at the trees and branches, live and otherwise, in my local meadow which I posted about recently, revealed large quantities of lichen. I’d seen it there before but never really paid it sufficient attention so a couple of weekends ago I decided to rectify this shabby state of affairs.
To my highly untrained eye there didn’t seem to be more than 4-5 species but the ones that were there were present in abundance. There are four basic morphologies of lichens: they are crustose – the flat ones which form very thin layers, foliose – form leaf like structures but where the leaves lie flat and don’t protrude far from the surface of the substrate, fruticose – have longer branched structures and can look like small shrubs and lastly squamulose – have horizontal, scaly, overlapping lobes and look rather like some fungi I’ve seen growing on dead wood.
Lichens can be extremely sensitive to pollutants, and as a rule of thumb the foliose species are generally more sensitive and are only found in places where the environment is clean and free of fumes and other chemical pollutants. Consequently the species I find in my local patch, being close to a big town, are of the crustose and fruticose varieties. Sensitivity to pollutants can cut both ways though, those susceptible to acid pollution will obviously suffer in a low pH environment, but others which have a high demand for nitrogen can really benefit from pollution by agricultural fertilisers.
The ones I found were all growing on the surface of live deciduous trees and dead branches and the trees in the meadow are predominantly ash and oak. I’m not going to try to identify the different species here because I don’t have the requisite expert knowledge to unambiguously name lichens, but I plan to do some reading and observing and I’ll post again if I find out what they are. Even though I don’t know the species I think their colours and structures render them particularly photogenic.
The ‘thallus‘ (main body) of the yellow lichen above has the leafy structures of a fruticose species surrounding round saucer shaped structures which are called ‘apothecia‘ and are the reproductive machinery of this lichen. Within the apothecia are tiny structures called ‘paraphyses‘ and these surround the ‘asci‘ from which the fungal spores are generated. Masses of this yellow species covered many trees and fallen branches in the meadow.
The fungal spores produced from the asci are microspcopic and dispersed on the wind and it is a matter of conjecture how they manage to settle on the requisite species of alga to form a new lichen.
Some species can reproduce both the fungal and the algal part simultaneously by growing structures called ‘lobules‘ or ‘isidia‘ which basically consist of outgrowths of the thallus of crustose or foliose lichens which break off and are dispersed by wind and water. Or there are structures calles ‘soredia‘ which are algal cells enmeshed in a bundle of fungal ‘hyphae‘ (threadlike structures of fungal cells) which are similar to the middle part of the body, the ‘medulla‘.
If anyone out there knows the names of these lichens or has any other snippets of lichen related information please leave a comment as I’d be very interested to hear them.