Working in grasslands, a lot of things seem to have a sweet hay scent, a bit like vanilla, which I presume is usually caused by coumarin or perhaps a derivative. This time of year, I can usually be found nibbling on a stalk of sweet vernal grass (Anthoxanthum odoratum), pretty commonly found in all but the most pristine grasslands. It’s the same chemical that gives flavor and odor to tonka beans, sweet woodruff, and hay-scented fern.
I’m indebted to Emily Tinalli, of Mt Cuba Center, for showing me that prairie dropseed (Sporobolus heterolepis) has a delicate odor when flowering. We get some big monocultures of it in places on the serpentine barrens, and you can definitely smell it wafting off the grassland in fall. I find it similar to the coumarin/hay odor, but others have compared it to coriander and buttered popcorn.
I tried smelling a carrion flower once. (Smilax pulverulenta or S. herbacea.) Description is accurate, 0/10, would not repeat; it was putrid!