From email@example.com on behalf of Tom Elpel
I think it is safe to experiment with unknown plants as long as you can positively identify the few plants that are absolutely deadly, like water hemlock (Cicuta), hemlock (Conium) and death camas (Zygadenus). (Would anyone add other plants to this list?) As long as you can rule out these few serious plants then it would be somewhat difficult to kill yourself with the rest of the plants out there (although you might make yourself seriously sick).
A better approach than randomly sampling the vegetation is to experiment with unknown plants only in known plant families. Genetically related plants usually have similar characteristics for identification and they often have similar properties and uses. If you know the key patterns of a family then you can recognize a member of that family anywhere in the world.
The Mint Family is an easy example to use in this medium. The plants have opposite leaves (found in pairs with one leaf on each side of the stem, as opposed to alternating along the stem) and distinctly square stalks. (I won't describe the flowers without an illustration).
You do not need to know the precise name of a specimen as long as you can positively identify it as a member of the Mint Family. Most members of the Mint Family are rich in spicy volatile oils, and hence many can be found in the spice cabinet, including: rosemary (Rosmarinus), lavender (Lavandula), marjoram (Origanum), mint, peppermint, and spearmint (Mentha), germander (Teucrium), thyme (Thymus), savory (Satureja), horehound (Marrubium), sage (Salvia-not sagebrush!), and basil (Ocimum).
After giving you this list of names, let me repeat that you do not need to know the individual names of the plants, as long as you can identify the family. Certainly the potency of the volatile oils is going to vary from species to species--some mints have no aroma at all, while others will overwhelm you from ten feet away, but you can identify potency--and hence the uses--with your basic senses, without ever knowing the specific name of a plant.
Granted, not all plant families are as consistent as the Mint Family, but knowing the families will at the very least help you to know which plants to be wary of. For example, the Parsley Family includes many edible plants like carrots, parsley, celery, and most of the spices in your kitchen that are not from the Mint Family. But, the Parsley Family also includes the deadly Cicuta and Conium mentioned above. When you identify a plant as a member of the Parsley Family then you know you must get positive identification of the specimen.
The essential identifying characteristic of the Parsley Family is the "compound umbell" of the flowers. The flower cluster looks like an umbrella stripped of all the webbing, with the spokes pointing upwards. At the end of each spoke is another smaller "umbrella", again with the spokes pointing upward, but with one small flower at the end of each spoke. (It is really simple once you see an example, and it is so distinctive that you will never forget it.)
There are an estimated 300,000 to 800,000 species of plants in the world, but only about 300 families (many more if you include the subfamilies that are sometimes separated out). Across the northern latitudes there are only about 100 families of plants, which are a whole lot easier to learn than trying to identify all the tens of thousands of plant species.
One of the problems in teaching primitive skills classes is that some students travel a thousand miles or more to attend a class, so the plants at home may be significantly different than the ones that are taught where the school is. It is somewhat useless to learn specific plants in that circumstance. Learning the families gives you much greater versatility to "know" plants where-ever you are. Dave Wescott at Boulder Outdoor Survival School arrived at a similar conclusion and started teaching families in their programs. He started compiling information on plant families for B.O.S.S. classes, but did not have the time to write a full book on the subject, so I did. Since I do not know of any other amateur-oriented books on plant families I will go ahead and give a plug for mine! The new user-friendly edition is called Botany in a Day: Thomas J. Elpel's Herbal Field Guide to Plant Families.