I’m sure few people will recognize that the title of this post was taken from Robyn Hitchcock’s second solo album, but it seemed appropriate nonetheless.
Several weeks ago, I collected some quaking aspen (Populus tremuloides) leaves to try to raise the agromyzid fly larvae that were mining within them. The larvae exited to pupate, and when the leaves had turned brown I removed them from the vial to reduce the likelihood that the puparia would become consumed in mold. To make sure no puparia or parasitoids were still in or on the leaves, I was holding the leaves up to my desk lamp one at a time, and I was surprised when this pattern appeared in one of the backlit leaves:
I have no idea what’s going on here. An internet search of “concentric leaf spot” produces this vaguely similar photo illustrating “tomato spotted wilt virus.” So maybe this is caused by a virus, but it might also be a fungus or bacterium. Whatever it is, what I’m really curious about is how it’s producing this crazy pattern.
Edit, 10/24/2019: I see that the above tomato virus link is now dead, and I’m not sure if this one will work if you don’t have a Twitter account, but it shows a similar pattern of concentric rings on a chestnut oak leaf, caused by Cristulariella leaf spot (a fungus).