I’ve found that wood nettle (Laportea canadensis, Urticaceae) seems to be one of the dominant understory plants in at least one local floodplain forest. Together with stinging nettle (Urtica dioica, Urticaceae) and giant ragweed (Ambrosia trifida, Asteraceae) these large plants create a dense jungle of foliage.
Although wood nettle possesses stinging trichomes like those found on stinging nettle, in my personal experience the sensation isn’t nearly as painful. In both plants the trichomes are composed of silica (think glass) and when brushed they break off, injecting irritating chemicals into the skin.
Wood nettle seems to serve as great cover for a number of arthropods, especially harvestmen (order Opiliones) and mosquitoes (family Culicidae). Whenever I walk through the dense stands of this plant, I often stir up large numbers of them.
The larvae of several butterflies also feed on wood nettle. You can see evidence of herbivory on the lower leaves in the photo above.