When I went to Londonthorpe to look at the winter buds, I noticed how well lichens had already established on some of the ash trees. These are often overlooked but well worth further investigation, especially if you have a little hand lens to help you out!
Definitive identification often involves recourse to complex keys involving chemical tests and microscope work. But don’t let that put you off, the more common species are often identifiable using a simple guide such as the ones produced by the FSC. These show you some of the species you often encounter along with the places you are likely to find them. For example, all three species shown below are found on the ‘Lichens on twigs’ laminated sheet.
Lichens are quite unusual in that they are a symbiosis between a fungi and an algae which are in entirely separate kingdoms – the plant and the fungi. They grow on trees, on stone, on sawn wood and bricks and even at the edge of the pavement where feet rarely tread.
A common myth is that lichens only grow where the air is clean. Whilst it is true that many species are very sensitive and can be used to indicate the quality of the air, there are also species which are quite tolerant of poor air quality and will thrive in fairly grim conditions. This is evidenced by the number of lichens you can find on trees in the busy London parks. All three of the species described below are fairly tolerant of nitrogen and acid pollution so we can’t use them to make any great claims about the cleanliness of Grantham! These are common species and are often the first to colonise new trees, especially smooth barked species such as the ash.
There is lots of terminology associated with lichens – the Natural History museum website has a good glossary. I will introduce a few of the key terms here which we can hopefully expand on with different species in a later post!
Lichens can be categorised as crusteose, those which form a crust upon a surface, foliose which are leafy in nature and fruticose which you could describe as shrubby. The three below show examples of crusteose and foliose species. I will try to add a fruticose specimen in a later post!
The xanthoria genus of lichens may be the ones you are most familiar with – you can find them in a variety of habitats and they are quite common. This species, Xanthoria parietina, is a foliose lichen and is a good model on which to show the difference between the main body of the lichen, the thallus, and the fruiting bodies, the apothecia. The fruiting bodies in this species are of the ‘jam tart’ variety, named because of their shape. These are where the spores, the reproductive seeds of the lichen, are produced.
Leacanora are crusteose lichens and are another fairly common group of species which you are likely to come across. This one is differentiated from the very similar Lecanora chlarotera by the colour of the fruits which are white rather than buff. Again, you can see the jam tart like fruiting structures and you can see the difference between this crusteose lichen and the much leafier foliose Xanthoria parietina.
You might have to look a little more carefully to spot this one, another crusteose species. Depending on the tree you find it on, it may only be the black fruits which give it away – these are often called wine gum fruits. If you look carefully though, you’ll see plenty of established specimens of this lichen on the ashes throughout the plantation, as well as tiny patches which are only just beginning to establish and where only a few black dots are apparent.