An oil called urushiol causes skin irritation when you brush up against this 3-leafed plant, Rhus radicans
... "Rhus plants(poison ivy, poison oak, poison sumac) are the most 
common... [DOC] [TLE] How to recognize plants that are poisonous to touch | Outdoor ... [PAR] Apr 30, 2014 ... Know how to identify these common poisonous plants when hiking.