Today I'm excited about: Yaupon Holly (Ilex Vomitoria)!
This little bush is native to the American South. It's the only known North American native to contain caffeine. Indigenous folks made tea out of it. It's related to yerba mate.
It's been "rediscovered" by white folks, and you can now buy the tea. It's quite good- mildly floral, somewhere between chamomile and mate in my experience. (As an aside, I'd love to know of any indigenous folks selling this as tea).
Yaupon is not native where I am, and somewhat marginal to my growing zone, but I'm gonna plant a bush or two this spring and see what happens! I'd love to grow my own (caffeinated) tea, and so much the better if it's native to areas relatively nearby. (And lord knows that the changing climate is only going to drive it further north).