I recently reviewed a book about lichens. It’s a small book, so only an introduction to an extensive topic. Finding a greenish-grey lichen similar to a photo in the book, on a hawthorn tree in my yard, drove my curiosity to learn a bit more about these organisms that are neither plant nor animal.
Lichens are made up of fungus (the protective outer layer), with algae and/or cyanobacteria (living on the inside and providing energy through photosynthesis) that work together in an association called symbiosis. They need each other to exist since they don’t have leaves, stems or roots. They absorb rainwater, and go dormant in dry periods.
My Scarlet Hawthorn tree has long puzzled me. It’s about 20 years old, produces a healthy crop of leaves each spring, and then bursts out in a profusion of glorious watermelon red blossoms.
But most years, it begins to drop leaves in July, and often by the end of August it is half bare. It doesn’t appear to be diseased, but I think it does suffer stress that depends on rainfall….and I haven’t figured out its favorite environmental condition. And it does have lichens….could they be harming it?
But lichens produce their own food, and since those that live on trees cling to the surface and don’t penetrate the wood, they are not thought to harm a tree. They seem to like older trees whose bark has cracks and uneven surfaces. When mine loses many leaves during summer, it gives the lichen more sunlight for its photosynthetic process. Since lichens can indicate good air quality, maybe they’re telling me something useful. They are food for some animals, like deer (they visit my yard) and might be a source of nesting material for birds (like the Pacific-slope Flycatchers that nest here every summer lately).
So I’ve identified this lichen as Fruiting Honeycomb Lichen (Hypogymnia lophyrea) based on a photo and description. It’s a foliose lichen, the most common type to grow on tree trunks. If anyone knows it is a different species, please let me know!
Gillian Richardson...naturally 