On the northern half of the trunk of an oak by the Lower Lake a coating of powdery green algae shows up in the morning sunlight. It is absent from the sunny south side of the tree so, if you’re trying to do a bit of natural navigating and you’re lost deep in the forest this could help you to orientate yourself.
This is probably Pleurococcus or a very similar-looking species of green algae. Seen through a microscope, Pleurcoccus is a globular single-celled alga with a thick cell wall to help it resist desiccation. The individual cells are slimy and stick together to form the powdery coating.
Green algae contains two kinds of chlorophyll: Chlorophyll A and Chlorophyll B. The two molecules work together; Chlorophyll A absorbs blue-violet and orange-red light while B extends the spectrum by absorbing blue light. The green that we see is the light that doesn’t get absorbed.