Definitely the most important plant to be learnt by any resident or visitor to the Peninsula or Outer Coast Ranges. It has leaves in threes, shiny and bright green turning to brilliant red in the fall. Flowers are dioecious, male and female flowers growing on separate plants. Poison Oak can grow as a creeper, climber or as an ordinary shrub. All parts of the plant secrete an oily resin (urushiol) which is capable of causing an extremely unpleasant rash if contact is made with the plant, with clothes that have been in contact with the plant or dogs that have been in contact with it. Inhaling smoke from burning Poison Oak can also induce a reaction. There is a popular saying, inaccurate but worth remembering — “Leaves of three, let it be”.