LICHENS AT TRUMPINGTON

Some soggy lichens at Trumpington, 23rd September 2012

It would be difficult to imagine a colder and wetter September afternoon. Not only does wet weather hinder the taking of notes but it also reduces the distinctiveness of lichen species. Subtle surface textures and characteristic colours are obscured when lichen thalli are wet. Nevertheless it was decided that an attempt at recording would be made and the chemically treated perimeter fence of the Park and Ride yielded some of the characteristic lichens of such toxic wood. Lecanora stenotropa is virtually indistinguishable from L. polytropa in the field and it is the latter which is commonly found on sandstone headstones in churchyards. If it were not for “tanalised” fences the former would have very few records but it seems to be the consistently occurring member of this pair on such woodwork. A specimen was collected and confirmed as L. stenotropa on the basis of its narrow spores. L. stenotropa not only tolerates the copper compounds used as wood preservative but actively accumulates it in its tissues and the fruits of this lichen had a visibly blue tint even in the abominable conditions. Jonathan pointed out a fascinating feature of these lignicolous thalli – their elongated oval shape. We are familiar with similar shaped thalli on young tree trunks where the regular radial growth of the lichen is distorted by the expanding girth of the trunk. In the case of elongated thalli on fence rails the mechanism is not so easily explained – obviously the fence rails are not expanding in any dimension. The long axis of the thalli were seen to be consistently parallel with the wood grain and so some feature of the lichen’s development must make it grow more rapidly with the grain than across it. An even more consistent lichen of chemically treated wood throughout Britain forms extensive granular crusts with minute pinkish pycnidia. This was well developed on the fence at Trumpington Park and Ride. Despite the fact that it is common and widespread its exact identity is not yet known. The filiform conidia make us confident that it belongs to the genus Bacidia but the lack of fruits has prevented a specific diagnosis. It will be interesting to see how this problem is resolved. Perhaps some apothecia will be discovered or else genetic sequencing might reveal its relationships. I tentatively suggested that it might be a well-known species such as B. saxenii whose fruiting is suppressed by the toxicity of its chosen environment. Jonathan made the interesting suggestion of transplanting some to a non-toxic substratum to see if this would stimulate fruiting. Although lichens can be remarkably hardy (Xanthoria parietina survived ten days in the hostile conditions of space hanging outside the International Space Station) they are notoriously fickle and temperamental if any attempt at transplantation is made. I doubt whether the sort of transplantation studies which have proved so useful in elucidating the taxonomy of vascular plants will work with lichens.

Species recorded at Trumpington P&R TL441541

Although rather recent, the concrete curb stones of the car park have beautiful mosaics of species such as Caloplaca oasis, C. saxicola, Candelariella aurella, Lecanora albescens, L. dispersa and Verrucaria nigrescens with “macros” such as Xanthoria elegans and X. parietina forming more conspicuous and three dimensional ornamentations. It was on a similar curb with a very similar community of lichens at an industrial estate in Northampton that I found the first authentic British specimen of Caloplaca soralifera earlier this year. This illustrates the intrigue of concrete. Most times what is found is a familiar suite of ubiquitous lichens but once in a while something remarkable turns up. Today the conditions were not conducive to finding rarities and it was decided that a brisk walk to the motorway bridge might generate some internal warmth.

The aluminium railings of the bridge over the M11 have a dark scurfy crust which could easily be mistaken for an algal crust or for “grot”. Careful examination with a lens reveals dark, convex fruits and my suspicion of Scoliciosporum umbrinum was confirmed when microscopic examination of these fruits showed that twisted S-shaped spores, spirally arranged in the ascus were present. This lichen is rather common on sandstone headstones but also has a more specialist ecology and has been found on “bare” aluminium of bridges at Waterbeach Airfield and at Great Staughton. The most abundant lichens on the tarmac and concrete of the bridge are Aspicilia contorta subsp. contorta and Caloplaca crenulatella. The only cyanolichen of the day was found on the northern footway of this bridge but, other than the presence of apothecia, little could be distinguished about its features in the field under a thick film of water. It was tempting to write it off as something like Collema tenax but a specimen was collected and subsequent microscopic examination showed that a cellular cortex is present. The tentative determination of this specimen is Leptogium turgidum but further work is required.

Species recorded on the motorway bridge TL441541

Examination of concrete retaining walls at Shepherd’s Cottage yielded only a limited community of lichen species but it was interesting to observe the “ghosts” of various phases of inundation of these concrete panels (by piles of spoil etc.) still delimited by abrupt variations in the lichen communities.

Species recorded at Shepherd's Cottage TL434538

Byron’s Pool, TL4354, 21st October 2012

One of the mature oak trunks yielded a surprise in the form of Enterographa crassa which is a lichen species which is listed in the Revised Index of Ecological Continuity; it is considered to be a poor coloniser that is usually restricted to ancient sites. Together with Opegrapha vermicellifera and Schismatomma decolorans these species probably represent a relic community which survived on sheltered tree bases during the many decades of severe atmospheric sulphur dioxide pollution. Porina byssophila has, until recently, been considered to be a nationally scarce lichen of siliceous rocks but recently it has been realised that it is not uncommon on tree bases, at least in Eastern England. Chaenotheca brachypoda is an attractive “pin-head” lichen with bright yellow-green pruina covering the spore mass. An enormous colony was found on the underside of a gently sloping willow trunk. There are microscopic features which differ from the description of this lichen species in the literature and one must always keep an open mind for the not infrequent discovery of new taxa for the British Isles. Lecanora barkmaniana is one of the “new” lichen species of which no evidence can be found before the 1980s. L. barkmaniana was described as new to science in 1999 and seems to be spreading and thriving in the modern eutrophicated landscape.

Species recorded in Byron’s Pool LNR:

Trumpington Meadows (within TL43.54)

The available substrates for lichens are rather sparse but records were made from concrete, an iron manhole grille as well as various trees. Opegrapha viridipruinosa was described as new to science in 2011 and good colonies were found on adjacent tree trunks beside the River Granta, one ash, the other willow. The ash trees on the embankment of a disused railway track supported only a modest lichen mycota but the presence of Lecanora confusa and Fuscidea lightfootii show how quickly the lichen communities are changing – both have only appeared in Eastern England in recent years. Short posts supporting rabbit netting beside the M11 barrier have extensive algal crusts but with colonies of fertile lichen thalli intermixed. In the field the possibility of a species of Vezdaea was mooted but microscopic examination show this to be a species of Bacidia, probably B. chloroticula.

Species found in this northern part of Trumpington Meadows:

Trumpington Meadows (within TL43.53)

Bare clayey ground and a track yielded our only glimpses of cyano-lichens with two taxa of Collema. Vertical wooden boards of a revetment beside a punt-house support an extensive sorediate crust of a species of Caloplaca – the under-recorded and misunderstood C. phlogina is the most likely candidate. On wooden rails made of former telegraph poles support a spectacular lignicolous community whose composition is similar to that found on sandstone gravestones. A lecideine species was not recognised in the field but turned out to be exuberant Catillaria chalybeia. The specimens of various mysteries and uncertainties from today will be retained in my personal herbarium; eventually taxonomic problems are sorted out but there is a long way to go.

Species recorded in the southern part of Trumpington Meadows (TL4353):

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