One native plant that you need to know about and be careful of is poison oak. This plant exudes a chemical that causes a rash, raises blisters, and serious cases cause swelling. The Poison Oak rash is cause by a chemical called urushiol. This is present in poison oak leaves, branches, roots, everything. When you touch it, the oil is absorbed into the skin. This is a poisonous substance, and the rash is the result of your body's immune system fighting against this invader.

Poison Oak can be in the form of a bush, a vine, or a root. Early in the year you may only see bare twigs with no leaves to speak of, but these twigs have the oil in them and can give you just as much of a rash as leafed out plants. I don’t have a picture of this stage because the poison oak just looks like most other twigs. Later, green leaves appear like in the first picture. Late in the season, the leaves turn red like in the second picture.