Truth is, of course, that the word might be Shushi, Susi, Sushi or Shusi. Anyhow, now that I did look up the Targum Laaz, I am glad to announce that it is actually fern. Thanks to Michael Wiener’s (Savage) book, Earth Food Earth Medicine, I was able to understand the Me’iri. Wiener writes that the Native Americans would eat young fern. Once it is old it becomes bitter and possibly poisonous.
The Shvatzri is wormwood, or flea-bane according to Rebbe Machir. I don’t recall bumping into any of these.