We found 2 Reddit comments about The Physicians of Myddfai. Here are the top ones, ranked by their Reddit score.
Physicians of Myddfai (mediaevil Welsh herbal cures): http://www.amazon.com/Physicians-Myddfai-Rhiwallon/dp/1479347116/ref=sr_1_1?s=books&amp;ie=UTF8&amp;qid=1452802247&amp;sr=1-1
Paul Beyerl's "Master Book of Herbalism" - highly recommended: http://www.amazon.com/Master-Book-Herbalism-Paul-Beyerl/dp/0919345530/ref=asap_bc?ie=UTF8
"Poisonous Plants and Fungi" - for the specialist! (UK based): http://www.amazon.com/Poisonous-Plants-Fungi-Illustrated-Guide/dp/0112427189/ref=sr_1_1?s=books&amp;ie=UTF8&amp;qid=1452802576&amp;sr=1-1