This photo, from my recent and gallette-packed French summer holiday, shows the distinctive orange lichens that have daubed a southern-facing wall of Suscinio Castle in Brittany.
Being a coastal region, Brittany is a natural home for these orange Xanthoria lichens, which can be both a blessing and curse when it comes to using them to understand direction. This is because conditions need to be close to perfect for lichens to thrive, but if they are too good then a lichen will manage well on more than one side, and occasionally on all sides.
This nuance creates a challenge for those new to the subject of natural navigation, including those who took part in the upcoming BBC2 series, ‘All Roads Lead Home’. Sue Perkins, in particular, was understandably frustrated that the lichens would not always obey a perfect rule in terms of the aspect they preferred. In the very short time available, it was incredibly difficult to convey the rich way lichens can help us navigate.
The important point is that lichens do not care about our concepts of north, south, east or west, they care only about their environment. South-facing walls, rocks and bark will tend to be drier as they receive more direct sunlight than north-facing ones (in the northern hemisphere). These sunny, dry conditions are ideal for these orange lichens and so there is a strong correlation between orange lichens and south-facing, but, and it is a big but, the keys lie in patterns and assymetry.
It takes time and patience to appreciate that hard rules are pointless when it comes to lichens, as lichens are as mischievious as they are fascinating: rules will deprive us of both confidence in direction and a richer understanding of our environment.
It is only by spotting patterns, getting to know consistencies – and indeed inconsistencies – that we grow to understand the habits, ie. habitats, of the lichens in each area.
Close to the sea these orange Xanthoria lichens are often happy to cover all sides of the right types of rock, but further inland they can be fussier, showing a marked preference for the sunnier southern side. Further inland still, they become rarer altogether. But they will tell a story of environment in each place, one that is fun to read, providing you resist the temptation to jump to the final page of the story by assuming rules and tricks that are not part of the plot!