While searching the woods for plant galls I came across these beauties on the leaves and petioles of Clematis virginiana. On the petioles they curled into various shapes and it was obvious they weren't galls. Measuring less than half an inch long, it required magnification to appreciate the tiny orange cups that covers the surface. Tiny round ones were on the underside of the leaves and the vines didn't seem damaged otherwise.
The knobs under the leaves were just miniature versions of the petiole growths and with magnification they too were covered with the little cups. Some sources refer to them as pustules but that seems to be a harsh judgement to me. Another term is a rust fungus, not much kinder name.
I think this is Puccinia recondita also refered to a wheat leaf rust, a fungal disease that is a major problem for farmers.
Gardeners consider it a disease on clematis but to me it is just another interesting small feature of nature, a mushroom on a leaf. In the words of Bill Bryson, "Life just wants to be, but it doesn't want to be much."
