I was in Delaware in March for a family reunion. Spring having emerged from winter the week before, there was much floral and insect activity. All the usual suspects started blooming. I went into a thicket down my cousin’s backyard and found this plants with interesting leaves with brown spots all over underneath.

At first I thought it was some kind of infection, but the spots were too regularly distributed. Under the foldscope each of those brown spots had a fan-like structure and interestingly they always surrounded stomata .

Upon scanning the field, I found several developmental stages of this structure. Video follows where I am discussing this with some kids.

It was then I remembered this remarkable post on Peltate trichomes by Manu, and his analysis on how this structure is used to trap moisture. See https://microcosmos.foldscope.com/?p=13025 . The physics of this process as explained by Manu is really interesting.
Currently based on my reading, I suspect this is a  member of the olive family (Olea), although the genus requires a bit more work, and another trip to Delaware. Dont forget to look under leaves, I have always found surprises.