Lichens

Lichens consist of a symbiosis between an algae and a fungus. The algae contains the pigment chlorophyll which it uses during photosynthesis to produce carbohydrates. These are required by the algae itself but are also absorbed and used for growth by the fungus. Thus the fungus obtains nutrients from the algae, the fungal tissue in turn may provide shelter for the algae allowing it to grow in harsh conditions such as rock surfaces where it would otherwise be destroyed.

Most of the lichens in the churchyard are crustaceous species, forming a crust over the substrate, and may grow as little as 1mm per year. In other, less polluted and wetter, parts of Britain such as the west coast of Wales and Scotland there are many leafy (foliose) and shrubby (fruticose) lichens which can grow at several centimetres per year. Some of these used to be collected on a commercial scale for dying wool. Indeed our own bright orange Xanthoria parietina was also used in medieval times as a remedy for jaundice.


Some notes on the cryptogams within the churchyard at the OU

by Richard Tofts

Churchyards are of acknowledged importance for lichens in Britain, and the British Lichen Society's Churchyard Project is now well under way. Churchyards provide one of the best and longest established 'outcrops' of stone in lowland England, and many different types of stone may be present in a small area, each supporting characteristic species of bryophytes (mosses and liverworts) and lichens.

Detailed survey work is yet to be done in the Open University churchyard, but some notes on the preliminary findings are provided below. Lichen names follow Purvis et al. (1993), those of mosses follow Smith (1978).

Calcareous rocks support the greatest range of species in the churchyard, with upper surfaces of gravestones and tombs being particularly subject to nutrient input from rainfall, bird droppings etc. In such situations, lichens species include Physcia adscendens, P. tenella (a species usually found on trees), Phaeophyscia orbicularis, Diploicia canescens, Candellariella medians (very rare on natural calcareous rock outcrops, but common in S.E. England on tombstones etc), Xanthoria calcicola, X. parietina, Diplotomma alboatrum, Physconia grisea, Tephromala atra, Lecanora muralis and L. dispersa. Foliose species are mostly absent from the vertical faces of the limestone memorials, their place being taken by crustose or placodioid species such as Caloplaca flavescens. The upper surfaces of limestone monuments provide a substrate for mosses such as Tortula muralis, Grimmia pulvinata, Orthotrichum anomalum, O. diaphanum and Homalothecium sericeum.

Acid stones support quite a different flora of lichens and mosses, with species including the lichens Psilolechia lucida, Candellariella vitellina, Leproloma vouauxii and Buellia punctata (a species more often found on trees and posts), and the moss Ceratodon purpureus.

Most of the lichens and mosses mentioned above are relatively insensitive to atmospheric pollution, but the presence of species such as Xanthoria parietina, X. calcicola and Diplotomma alboatrum suggest that the site now lies no lower than Zones 4 or 5 of the Hawksworth and Rose scale (winter SO2 concentrations of about 60 µg/m3). Atmospheric concentrations of SO2 have fallen in the locality over recent years, and it seems quite possible that we might expect an increase in lichen species diversity in the future. On a group of poplars close to the churchyard several depauperate specimens of an Usnea species (apparently Usnea cornuta) are present, growing in association with Evernia prunastri. Usnea species are indicative of low atmospheric SO2 levels, and the specimens at the Open University appear to be recent arrivals.

The British Lichen Society has published an excellent leaflet entitled 'Churchyard Lichens', and details about the Churchyard Project are regularly given in the British Lichen Society Bulletin (eg No. 74 pp 43-53, No. 75 pp 28-33, No. 76 pp 21-27).

If you would like to learn more about bryophytes or lichens, why not contact or join the appropriate Society? The addresses are given below.

British Bryological Society. Department of Botany, National Museum of Wales, Cardiff. CF1 3NP, U.K. For membership details contact the Membership Secretary: Mr A.V. Smith, 1 Carr Meadow Cottages, Glossop Road, Little Hayfield, via Stockport, Cheshire, SK12 5NR.

British Lichen Society. c/o Department of Botany, Natural History Museum, Cromwell Road, London, SW7 5BD, U.K. For membership details contact The Secretary at the above address.

References

Purvis, O.W., Coppins, B.J. and James, P.W. (1993). Checklist of Lichens of Great Britain and Ireland. British Lichen Society Bulletin No. 72 (Supplement).

Smith, A.J.E. (1978). The Moss Flora of Britain and Ireland. Cambridge University Press.

Links to other lichen pages including the International Association of Lichenologists


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