It's been a strange year for my medicine garden attempts. Most of the seeds that I intentionally sowed did not even sprout, but some strange (to me) plants and flowers appeared without any help from me! Did my homework and was able to identify a few that most people call "weeds", but so far none of my plant friends know what this one is.

Description: Very fast-growing; it is now 4ft tall. The main stem is almost 1 inch in diameter at the base, and is fleshy not woody. No signs of flowering. Leaves are "feathery" and have a fresh herbal scent when crushed. Tastes sort of like a lettuce. High moisture content.

Any ideas?