I can't resist a question about food history, so I started to do a little searching. It appears that there were good reasons some of these foods disappeared (there usually is, with taste and ease being the prime motivators..
While I normally don't quote Wikipedia, since they're referencing Jared Diamond, this seems reliable. (The article does show a photo, however, which suggests it's still growing, if not domesticated, if you're determined to have some, but it looks like you'd have to just collect it, unless you find someone who's into wild herb craft.)
Here's the item on marsh elder:
"Iva annua (sumpweed or marshelder) is an herbaceous annual plant native to much of North America. Iva annua var. macrocarpa was formerly cultivated by Native Americans in the Eastern United States and specifically near modern day Illinois for its edible seed. As the author Jared Diamond notes, the edible parts contain 32 percent protein and 45 percent oil.
However, like its relative ragweed, Diamond notes that sumpweed possesses many objectionable qualities which include being a severe allergen, possessing "a strong odor objectionable to some people and that handling it can cause skin irritation." For these reasons Diamond believes that it was abandoned once more pleasant alternatives (like corn) were available, and by the time Europeans arrived in the Americas had long disappeared as a crop."
An interesting note on the Jerusalem artichoke (which you may already know) -- "Jerusalem" is a corruption of the Italian for sunflower -- girosole.
Another article says that quinoa is, in fact, a type of goosefoot -- the goosefoot family includes quinoa, as well as other plants, some used as herbs (such as epazote) and others as greens. So you'd need to find out which goosefoot was being consumed, as it's a large group.
Diamond's book "Guns, Germs, and Steel" mentions knotweed, along with little barley and maygrass, so you may have even more delicacies awaiting you.
I suspect you'll discover that sunchokes and sunflower seeds are going to be the tastiest items on this particular menu.