I use this book a lot, or did before I developed a good grasp of edible plants. It has a guide to plant parts in the front. This is a field guide, not a how to book.

Before you go picking edible plants- especially anything that looks vaguely like Queen Anne's Lace- you need to know what is dangerous. Most so-called poisonous plants are merely emetic- they make you vomit. But there are a handful of deadly ones (aside from mushrooms) and you need to know them. Be aware that even edible or medicinal plants can have poisonous parts.

Once you start learning edible and medicinal plants, you will learn that many are not identified as such, so you will want a good field guide to wildflowers.

Here is the West Coast version of the Duke field guide above. Also not a how to book.

Penelope Ody is British, but she gives clear directions in this well-illustrated book, the American edition of which is available used quite cheaply.

Learning to make herbal medicines is a long journey, but there is no reason why not to start. It is out of print, but I really like Debra Nuzzi's book which gives clear instructions and has a list of optimum alcohol contents for tinctures of various plants.

I have a soft spot in my heart for Bradford Angier whose Wildwood Wisdom started me off as a child. This is his field guide, more folksy and less systematic and just fun to read.

Tells you about how herbs are used, but you will need a field guide to identify them. Still a great introduction.

I think this book is the best of many many mushroom guides I have, but it really is too big to cart around in the field, which is a problem. Never collect mushrooms just based on books and always find books that have local species- the mushroom kingdom is rife with look alikes.