There is another mustard in our area that is smooth like bitter cress but is much larger, with leaves about 8” long, and typical mustard-yellow flowers—a variety of Winter Cress. I found some in the bed of Louse Creek, and spread the seeds in a few people’s gardens. It has taken hold in one but has shown no signs of taking over and becoming weedy, not being nearly as prolific as bitter cress.
I scattered store-bought water cress seed in a couple of water courses attached to ornamental ponds. I won’t do it again; it takes over and fills the water course with its spongy net of fine roots, holding the gravel as I pull it out. Water cress has short, thick lobed leaves on succulent stems that root as they crawl but stay under 3 inches tall, as well as spreading by seed.