This long rusty mark was found on a black cherry near our office in Corinth, Vermont. What caused it?
Answer
An alga (Trentepholia sp.). Trentepohlia is usually part of a lichen, but in this photo it’s “free living” - not associated with a fungus to make a lichen. A lichen is a combination of a fungus (the mycobiont) and an alga or sometimes blue-green bacteria (the photobiont). Trentepohlia is a green alga but it looks red (or yellow or orange) because the chlorophyll is masked by carotenoid pigments.
We thought for sure we’d get to keep our book this time around. But no. We had a number of correct guesses, proving once again that it’s very hard to stump our readers.
This week’s contest winner was Dave Houston