Answer: Believe it or not, I don't know the answer off the top of my head! But here are two books that might help. I found them via the online bookstore Amazon.com -- unfortunately, I think they are out of print but they may be able to track them down for you.
Shakespearean Plant Names : Identifications and Interpretations (Acta Universitatis Stockholmiensis. Stockholm Studies in English, 43.) by Mats Ryden
The Plant-Lore & Garden-Craft of Shakespeare by Henry Nicholson Ellacombe
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