Stinging nettles are a dioecious herbaceous perennial, growing to 1-2 m tall in the summer and dying down to the ground in winter. It has very distinctively yellow, widely spreading roots, rhizomes and stolons. The soft green leaves are 3-15 cm long and are borne oppositely on an erect wiry green stem. The leaves have a strongly serrated margin, a cordate base and an acuminate tip with a terminal leaf tooth longer than adjacent laterals.
It bears small greenish or brownish 4-merous flowers in dense axillary inflorescences.
The leaves and stems are very hairy with non-stinging hairs and also bear many stinging hairs (trichomes), whose tips come off when touched, transforming the hair into a needle that will inject several chemicals: acetylcholine, histamine, 5-HT or serotonin, and possibly formic acid.
This mixture of chemical compounds cause a sting or paresthesia from which the species derives its common name, as well as the colloquial names burn nettle, burn weed, burn hazel.
This sting can last from only a few minutes to as long as a week
No stinging nettles do not cause any smoke .
click on the links below for the images of the plant to make sure that the plants you encountered are really stinging nettles -
http://greenjacker.files.wordpress.com/2009/03/stinging-nettle.jpg
http://www.florahealth.com/NR/rdonlyres/7431AA90-1FD6-11D6-8E33-00B0D0AA4F55/3475/StingingNettle.gif
the sting - and the information =
http://www.wellcome.ac.uk/en/bia/gallery.html?image=18
Thank you !