I’ve been looking at ephemeral coatings on tree bark for awhile now, and here’s a colorful one, on one of the old beeches that we find in the southernmost reaches of the little feeder creek hollow. It’s not on all the beeches, but I don’t find it on other trees in the area. I don’t see it any farther up than about ten feet from the ground, and it seems to grow on the south to southwest side of the trees. It brightens up in the wet, and becomes a little more subtle as things dry out, which is how you see it here. Fairly extensive internet searches haven’t netted descriptive text, although I’ve seen a couple of beech photos that seem to have the epiphyte present, though unremarked. It’s a very thin yellow green layer unevenly coating portions of the bark.

A little closer, there still isn’t any structure, though you can tell some thickness to the coating. It had been several days of dry weather after a rain, so that may explain the powdery appearance.



I see three possibilities - an epiphytic cyanobacterium, a coincidentally yellow-green fungus, or that living symbiosis of the two: a crustose lichen.

Even crustose lichens usually show some symmetrical growth pattern, and at some level some morphological structure. Even at the closest my camera can come there just isn’t any recognizable (recognizable by me, anyway) structure.

Much, much closer: at this level there’s certainly a powdery aspect to it. It could still be a fungus, with the colors just coincidental rather than an indication of photosynthesis. Everything taken into account, if it’s not a lichen, I’d probably go with a cyanobacterial mat of some sort.



At any rate I doubt if it’s any indicator of disease. This seems to be a commensal epiphyte - the bark just supplies it with a surface to grow on. There is beech bark disease, but this isn’t it. I took some scrapings but despite the appearance the growth is extremely thin and I didn’t get much. I’ll try for some more after a rainy day, which should happen on Wednesday and Thursday.