Cololejeunea and Colura in Glamorgan

Cololejeunea miutissima (Minute Pouncewort), Afan Forest

After reading Graham's excellent update on Breconshire bryophytes, and particularly his comments on Cololejeunea minutissima, I thought it might be a good idea to review the apparent, current status of these two liverworts in VC41, at least according to Map Mate records.
Hilary and I encounter Cololejeunea quite a lot in NPT, and it's beginning to look as if it is distributed widely in the county. The apparent gaps in its distribution are probably more a reflection of recorder effort than anything else. You are as likely to see it on a tree in a park as on willow in a conifer plantation and I think we should look for it in every tetrad.

Cololejeunea minutissima is easy to identify particularly when it's in fruit. The perianths resemble the heads of a small Phillips screwdriver (fairly clear in photograph above). But even when it's not in fruit, the dense clusters, sometimes forming little mounds, are very distinctive. The rise and rise of this species in South Wales is very significant.

The rise and rise of Colura calyptrifolia is also significant.

Much of the distribution of Colura shown in the map above corresponds with the distribution of Sitka Spruce plantation in NPT. Sam's highly plausible theory that mature conifer forests provide the cool, moist conditions that this hyperoceanic liverwort enjoys, and also have acted as very effective traps for spores than have rained in on westerly weather fronts, goes  a long way in explaining the phenomenal expansion of this species' range in South Wales. Hilary searches diligently for Colura almost everywhere we go, so the gaps in its distribution in NPT at the very least suggest that it is rarer in lowland squares away from plantations. The exception seems to be areas in the vicinity of Crymlyn Bog and the nearby Tennant Canal where it occasionally grows on willows. It's apparent rarity in Gower is interesting; Barry tells me that he has searched for it, without success, in suitable places. In contrast, Cololejeunea minutissima, another hyperoceanic species, seems to be more common in lowland areas and its distribution does not correspond specifically with the occurrence of conifer plantation.
As the density of Colura increases in and around plantation areas, the increased propagule pressure may  generate a second phase of expansion. This may already be happening in areas of mid and east Glamorgan. 

Colura is often found on willows, particularly Salix cinerea, but it can be found on virtually any tree (conifer or hardwood, including Buddleja) in suitable locations. It also grows on Ulex spp., Calluna vulgaris and Vaccinium myrtillus in NPT, which are common hosts for it in Ireland. It has even been recorded growing on glass.
As the data base of records for South Wales bryophytes increases, I think it will reveal some very interesting and detailed patterns in the distribution of species like Cololejeunea and Colura. Since they are both bellwether species, whose current range expansions are indicating significant changes in our climate, we shouldn't underestimate the wider value of our efforts.