Poison Ivy

 

Photo: Matthew Richardson

 

Photo: Matthew Richardson

 

Photo: Matthew Richardson

 

Photo: Matthew Richardson

 
Not a tree, but a small erect shrub or tree-climbing vine.  Three-parted compound leaves which are variably toothed but have a pointed end leaflet on a longer stalk than the side ones.  Irritates the skin, can cause major problems for those who are allergic.