I agree with digigarden and I do not agree with Tim
I take a challenge in identifying the stinging nettle(Urtica dioica), it is not jamaican cherry(Muntingia calabura),the photo posted by jcaldeira
There will be no purple color hue on the jamaican cherry seedling.The leaves of it are more elongated and the shape of the leaves are not in zigzag fashion as that of stinging nettle(Stinging nettle plants are common in moist places).
This photo is of seedling of Muntingia calabura
This photo is of the branches of the same tree with a fruit under which the seedling is growing
If anyone wants seeds of Muntingia calabura,I will send ASAP
Roy