If you are suddenly faced with a long-term survival situation, isolated from other humans, stranded in the middle of nowhere, you will have to follows certain steps to ensure that you indeed survive even before thinking about rescue or escaping from your isolation; finding food would be one of your priorities, and plants may prove to be one of your obvious choices.
Plants are almost everywhere, even among rocks in high mountains you will find shrubs and little flowering plants like the fabled Edelweiss of the European Alps, and while hunting and fishing are indeed valuable and certainly effective means for gathering food. But these techniques have a number of disadvantages: first of all, if you are not an experienced hunter or fisher already, you will have a long, steep learning curve ahead of you because animals are not stupid enough to let anyone or anything catch them just like that, and you will have to learn how to lure them into a trap or the aiming line of a weapon.
Harvesting edible plants, on the other hand, is a very easy thing to do, and even wounded survivors, children and the elderly can participate in these emergency agricultural ventures; however, some plants are poisonous and can even kill a person, or they may cause you a lot of digestive problems. Others may not be edible or tasty as well.
The first rule for harvesting comestible plants is not to harvest fungi; these are not exactly plants but can be included in this discussion: some fungi are downright poisonous, others get poisonous as you cook them, in the case of others, they are poisonous raw but edible if boiled, and others look like different species than they really are. So identifying them is really a work left for the very, very desperate survivor that has nothing to loose and can play a Russian roulette of sorts, or for the specialist. Better leave mushrooms for the restaurant.
On the other hand, flowers are generally edible and taste pretty well; anyway, donít take anything for granted and apply the edibility test to flowers as in the case of any other plant in the whole or plant part. Be careful with the fact that in the case of many different plants, some parts may be edible, like its flowers, while at the same time other parts, like the roots or bulbs, may not.
It is very important to remember that the edibility test should be performed with various parts of each plant and even with plants that you already know but grow in a different place: local variations produced - for example- by minerals in the soil, may mean different degrees of potential toxicity.
Then, in order to find out if you can eat any given plant, cut a little piece and see what kind o fluids come out: if they are milky or pungent, chances are that the plant is poisonous. Taste a bit with the tip of your tongue; if the taste is strong or hot, better leave that plant alone, and if it is not, bite a little piece, chew it well and swallow. Then wait for about four hours.
If you star feeling funny in any way, discard that plant; if you feel nothing, take a fistful of that plant and eat it. Wait again, for four hours and if nothing happens, try a fistful of that again, making sure that you are trying the same species of plant; remember that you should perform the test with all different parts of each plant, like its flowers, leaves, roots, stems, etc.. If nothing happens after that, you can consider that particular plant as safe for human consumption.
But donít just rely on this article: This topic is extensive, and there are even a few books available about this particular subject; you will find links to various pages and products related to plant edibility within a survival context through this link.