At this time of year when leaves are falling off our deciduous trees, the abundance of mosses, liverworts and lichens that live as epiphytes on tree bark is much more apparent. Among the lichens, some of the most obvious are the larger, foliose species of Parmelia. But close inspection will reveal a beautiful mosaic of smaller lichens, especially on the smooth bark of twigs in well-lit environments. Arthonia radiata and Lecidella elaeochroma (shown in the photograph below, taken on a walk along the Old Railway Trail in Afan Argoed) are common on smooth-barked trees. At a glance they look similar, but under a hand lens you should see that A. radiata has irregular (sometimes star-like) shaped apothecia while those of L. elaeochroma are roughly circular [click on the image to see detail of these two species].
Lecanora species belonging to the Lecanora subfusca aggregate are also very common, especially L. chlarotera. Unfortunately, species in this group are often difficult to tell apart without microscopic examination. In the photograph below (which was taken near the parking area on Crymlyn Burrows), you can see L. chlarotera with the pale red brown apothecia (upper right) and L. argentata with the darker brown apothecia (upper middle) – the lichen on the upper left is Lecidella elaeochroma again. The apothecia of L. chlarotera have a coating of mica-like granules on their surface but those of L. argentata do not show this feature. L. argentata is very under recorded. Note that the apothecia of Lecanora species have a distinct white margin.
Physcia species are small, foliose lichens with narrow lobes. Two species encountered commonly on woody twigs are P. adscendens and P. aipolia. Both are very distinctive and the photograph below shows both species side by side for comparison. Physcia aipolia is the one on the left with the abundant, dark apothecia. In contrast, the thallus of P. adscendens produces prominent hair-like cilia and the ends of the lobes have a mass of powdery soredia. However, P. adscendens rarely produces apothecia. The lichen on the far right of the photograph is Lecidella elaeochroma again. All these lichens were found growing on young oak twigs near the car parking area on Crymlyn Burrows.
Large yellow patches of Xanthoria parietina are often found on the twigs and trunks of trees near our coast. Along the Coed Morganwg Way, near Bryn, exposed Larch twigs are covered with the smaller Xanthoria polycarpa. Note the abundance of apothecia which almost cover the thallus.
Also see: http://goweros.blogspot.com/2009/10/afon-argoed-lichens.html