This essay here is not a much updated piece of writing but here you will find some help as to what is fine for eating in wilderness and what is not. Some poisonous hemlocks have looked like carrots or parsnips and have killed people to much regret; therefore it is important that one realizes not to eat every familiar thing one might find in the wilderness.
Remember the following points when collecting plant food in the wilderness.
Pesticide sprayed plants:
People tend to pick easily the plants growing near dwellings and near populated areas. But beware that these might be sprayed with insecticides or pesticides therefore it is very important to wash whatever you pick before eating. Wash not only the picked plant but also your hands to get rid of any smells or chemicals that might have come on it while picking.
Plants that grow near lakes or ponds might be contaminated. Before eating any you need not only thoroughly wash them but also boiling for a disinfection purpose is required. Also some plants might grow very highly toxic fungi. Avoid them at all costs and do not eat any fruit that might have signs of yeast, mildew or algae growing on it.
Some people develop food poisoning or other gastric diseases very easily. If in any way you have a weak stomach avoid anything that looks unfamiliar. For example, some people need to avoid the poison ivy since that is heavy food. Or maybe some cashews or even mangoes since these foods can give you continuous urge to pass stool.
Bitter Edible Wild plants:
Some wild plants are bitter and not easily edible. This family includes acorns or maybe even wild lilies. If left with no choice, boil them to the highest degree and that will leave the plant without the tannin compounds which makes in inedible.
The most important thing to remember is that, even in extreme case of survival do not eat any mushroom plant. This plant is not for experimentation. There is no tried and tested method for experimentation on mushrooms. My advice to you is that even if you are hundred percent sure do not eat any mushroom. These plants have caused immediate deaths. Side effects include severe impact on the central nervous system to excruciating gastric problems. Some side effects or effects also occur after several days after which some times it becomes too late to reverse back the side effects.
If you are a regular hunter or tracker or just an adventurous person, I would suggest that you invest in some good handy book which guides you towards basic plant edibility in the wilderness. If in any other case, exercise extreme caution while eating anything unfamiliar and trust your instincts.