One thing I like to remind people who forage is that while learning all about edible plants is important, it is also important to know what is in the soil the plants are growing in. For example, plants growing near pressure treated wood structures probably have a high arsenic concentration. Also, many common edible plants are accumulators by nature and might have higher concentrations of chemicals such as nitrates, found in fertilizers used on fields and adjacent runoff areas. Just today a buddy and I were sitting on a log enjoying the sun looking out over a green field surrounded by pine trees. He started munching on some edibles when I reminded him that the field is the old landfill... who knows what heavy metals, etc. are in all those otherwise healthy edibles growing all over it?

Know your plants, yes, but know your soils too.