Here's where I've been spending a lot of time this past week, and will continue to for the next few weeks.
We've surveyed seven EEON plots this week and will continue on schedule next week. Aside from the Hypogymnia spp., the Usnea spp. can be a little tricky. We initially thought we had 3 different Usnea spp. from the first couple of plots, but as the week progressed I realized that we probably only had 2, U. cornuta and U. filipendula. Often we were stuck with small samples, so it was difficult to get a feel for the overall growth shape (tufted or pendulous) and had to look closer. Luckily, there is a quite a bit of difference between the axis (cord) of these two species.
The U. cornuta axis is thin compared to the overall width of the thallus. The medulla is very thin and 'wispy'.
Another distinguishing feature is 'cigar' shaped branches of U. cornuta.
Note the main branch and how the off-shoot branches are slightly pinched at the connection. I believe this is the 'cigar' described by McCune and Geiser.
Compare this with U. filipendula. The axis is much larger and the medulla is dense and white. You can also see the cortex is thick and papillate. The deeper green spots surrounding the cord are algae. The connection between the main branch and smaller branches is round without a distinct 'pinch'.