Within his report Andrew has recorded over 100 lichens living within our churchyard and I would recommend having a look at his report as it clearly shows where the variuos lichens can be found.
Lichens are dual organisms – a fungus enclosing an alga. Most lichenised fungi are dependent on the association and the dominant partner, taking over an alga to exploit it for the sugars it manufactures by photosynthesis. Though the alga may be capable of living independently, it also benefits from the partnership being able to survive in exposed habitats such as sun-baked headstones protected from strong light and desiccation. Nearly everything a lichen needs can be taken from the atmosphere or rainwater, so they require little from the substrate they grow on, though the chemistry and texture of e.g. stone or bark has a strong influence on the species which can colonise. For these reasons, lichens can be good indicators of the quality of the atmosphere and health of the environment.
In his conclusion Andrew stated- "Also, though nothing of exceptional rarity was found, this does not detract from the species-richness of the churchyard, or from the collective significance of particular species associations, most notably on stone and lignum. Churchyards such as St. Ippolyts are of county importance for locally uncommon species including those with very restricted and specific habitat associations such as Aspicilia calcarea requiring limestone of some antiquity and found here on the chancel windowsill. There is further potential for the future, both as a result of growing knowledge of what is already present and through the continuing colonisation of churchyard trees, mirroring the changing fortunes of Hertfordshire lichens."
Michael Hooper Feb 2015