A Modern Herbal by Mrs. Grieve's (Vol. 1 and Vol.2) and Paul Beyerl's Master Book of Herbalism.
It is very helpful (if you are able) to meet with a practicing shaman for initiation, or just to learn first-hand about methods and beliefs. You can find workshops and/or reach out to some here:
https://shamanism.org/workshops/calendar.php?Wkshp_ID=10
https://shamanism.org/resources/csc.html
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If this is not possible or if you would like to do some reading first, here are some books I'd recommend as they've been boons for my personal practice and understanding:
Specifically Plants:
(Not necessarily scientific, rather folklore based but still helpful.)
https://www.amazon.com/Modern-Herbal-Properties-Cultivation-Scientific/dp/0486227987/ref=sr_1_2?ie=UTF8&qid=1548647960&sr=8-2&keywords=modern+herbal (and the other volumes)
Shamanism / Journeying:
(A classic text on what shamanism is and how to practice.)
(An interesting read on how to apply and practice shamanism with modern-day technology and scenarios.)
(As in the title, this is very much a beginner's guide for journeying, but it is very concise and effective information. Comes with a CD that has journeying drum tracks on it, which are very good even after you are done reading the book.)
General Texts:
(If I could only buy one book from what I am listing it would be this one; it is also the cheapest on the list. Essentially, it is a distillation of how to instantly, though not without challenge in all likelihood, improve your mindset and therefore your life in the avenue of Toltec wisdom.)
(I am an active practitioner and community member following the Venerable Dhyani Ywahoo. Her first book describes the roots of her teachings which have been passed down for 27 generations. There are visualization and meditation techniques, symbolism for crystals and the directions, and other vital information for one interested in such things.)
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I hope I have been helpful in some way. May you have peace, love, and kindness and recall your true nature.