A Positive Reaction

Day 129: Well, this was fun! One of the methods of determining a lichen identification involves testing certain areas of the specimen with common chlorine bleach. A positive reaction (i.e., a colour change) can be useful for differentiating species.

My sample was collected from a Douglas fir (Pseudotsuga menziesii), the first clue as to its identity. However, I was not certain that I was observing a secondary interior exciple ring in the well-developed disks, a feature which would have solved the mystery in the field. The larger size of the disks seemed to rule out Trapeliopsis which is generally under 1.5 mm., but just in case I had a whole forest full of atypical specimens (not likely!), chemical testing was in order. Upon applying a drop of bleach to one disk, it turned distinctly red, as did the thallus when the bleach came into contact with it during a second test. Given that the specimen was taken from Doug fir and that it showed a C+ reaction in both the thallus and apothecia, I am confident in stating that the lichen in the photo is Ochrolechia oregonensis, Double-rim Saucer Lichen. Its close cousin O. laevigata (Smooth Saucer, featured previously in this blog) grows on deciduous trees as opposed to conifers.