As a comment about Stinging Nettle (Urtica chamaedryoides)
I came into contact with this stinging nettle this morning when I was weeding an area of the garden ... so I can attest to its common name of "Fireweed"! It causes an extremely painful stinging and burning sensation! Since I wasn't wearing gloves when I pulled a handful of weeds that contained the nettle, I got a good dose of the stinging on my right hand. I immediately ran inside and made a thick paste of baking soda and water, which I applied to my hand. The burning sensation subsided within 30 - 40 minutes, but even two hours later there's still a mild stinging sensation.
*** Note to self ... ALWAYS wear gloves when gardening!
This Nettle is native to the Southeastern United States and Northern Mexico. Here in Florida, Fireweed is often found in moist, disturbed areas, lawns, and pastures. The plants are usually avoided by cattle, but horses sometimes browse this plant, which can cause stress symptoms, such as breathing difficulty, difficulty swallowing, and weight loss. In extreme cases it can cause death in younger horses when they become exposed to the toxins by rolling around in the plants.