I went for a walk in the forest in search of new green vegetation. It is still a bit early, and for the most part, the forest still looks at rest. When I glanced down at this rock, however, I noticed bright red dots. On closer examination, I found there was an entire garden of moss and lichens covering the rock’s surface.
A bug’s eye view reveals a lilliputian world of vivid forms and colours, greens, yellows, silver and even bright red. The red dots are the tips of British Soldier lichen (Cladonia cristatella). A lichen is actually two organisms, an alga and a fungus, living in very close association. The algal component manufactures food via photosynthesis, while the fungus absorbs moisture and minerals. Most of the visible body of the lichen is made up of the fungus, with the alga forming a thin layer just below the fungus surface.
Lichens are ancient organisms that first appeared on the planet about 225 million years ago. Lichens usually grow on nutrient-poor surfaces, limiting their rate of growth. They are widespread, but are sensitive to air pollution. Thus, an absence of lichens can be an indicator of poor air quality. A second cladonia species was represented in the rock garden by pixie cup lichen (Cladonia chlorophaea). Pixie cup and British soldier lichens are fruticose growth forms. Of the three lichen forms, crustose, foliose and fruticose, the fruticose lichens are the most sensitive to air pollution and are the first to disappear as air becomes more polluted in an area.
Willow House Chronicles 
Interesting to learn about their sensitivity to pollution. I’ve always enjoyed coming across a crop of British Soldier Lichen; now there’s one more reason to be glad whenever I see them.
Thanks, you have helped me with my biology project.
It is actually interesting how they are so sensitive to air pollution.
Glad I could help, Tom. It’s strange but true that a lot of things get more interesting the more you learn about them.