Caloplaca aractina is a 'crustose' lichen; one with a crusty-like appearance. The body of the lichen (its thallus) is an oily dark brown to grey colour, which means it can be overlooked against the rock on which it grows. The fruiting bodies are slightly more obvious when they appear, being orangey-brown in colour, sometimes bright red though very small (less than 1mm).
Lichens have colonised some very extreme habitats, including some of the coldest and hottest areas of the planet. They are incredibly hardy organisms, able to survive for years on the minimum of water, and growing almost imperceptibly slowly. If you examine the colonies that grow on tombstones, you can work out the age of some of these patches of lichen. Tombstones usually have a date on them revealing the year that the bare stone became available for colonisation.
In the UK, the range of this lichen is limited to the Lizard Peninsular, Cornwall where it is quite frequent on coastal rocks. There are other records from the British Isles but these are now believed to be incorrect. It is also found along the coasts of western Europe and from inland southern Europe.
This species is not currently threatened, though it may be vulnerable to oil spill incidents on some of its sites. It is not fully understood why this species has declined so drastically over the last fifty years. Scrub encroachment might prove a threat at its only known site in the UK.
Caloplaca aractina is listed in the UK Biodiversity Action Plans and included in English Nature's Species Recovery Programme. The site on the Lizard where it is found is a National Nature Reserve, so appropriate management for the species does not pose a problem. However, with a species that has such a precarious status in Britain, it is important to find out as much as possible about its requirements. It is necessary, too, to make mycologists (fungi experts) aware of this species and encourage them to report any sightings of the lichen elsewhere. Part of the Species Action Plan for C. aractina is to compile a list of suitable sites to search for the lichen, and compile a database of endangered lichens. This might help other members of this fascinating group that are critically endangered.
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