Photo: 23 of 58, Album: Foraging in Prospect Park - July 09, 2000
Jewel weed. Water sticks on it like little diamonds. Rub on mosquito bites and they'll be gone in 15 minutes. Also for poison avy. If rubbed on before rash you won't get rash.
Scientific name: Impatiens capensis
More plant pictures at Jewelweed