Here are the steps to take to see if a plant/food item is edible in a survival situation:
1. Do not eat anything for 8 hours prior to performing the test, and then rub your selected piece in the bend of your elbow trying to get as much juice out of it as possible. If there is no rash, burning, redness, etc. after 15 minutes go on to step 2.
2. Rub your selected piece in the corner of your mouth, being careful not to get it in your mouth or on your tongue. If there are no reactions after 5 minutes move on to step 3.
3. Place a small portion of your selected piece on your tongue, and let it sit there for 15 minutes. If there are no reactions move on to step 4.
4. Thoroughly chew the piece from step 3 and hold in your mouth for 15 minutes. Take care not to swallow the piece of plant or your saliva during this step. Again, if after 15 minutes there are no reactions, move on to step 5.
5. Swallow the piece and wait 8 hours drinking only water. If you become ill, make yourself vomit and drink as much water as you can. If no adverse reactions move on to step 6.
6. Eat a handful of your selected piece and wait another 8 hours. If nothing happens, then your selected plant piece and method of eating it is safe.
The edibility test does take some time, so make sure you are in a safe location, close to potable water, and have enough time to do it. If you experience a reaction on your skin, rinse it thoroughly. If you become ill after ingesting it, you will need to induce vomiting and possibly experience diarrhea – hence the need to be close to potable water. This is a last resort to finding food.