Caper spurge. Leaf of the poisonous plant caper spurge (Euphorbia lathyris), also known as the gopher, mole or petroleum plant. If the leaves or stem of this plant are broken a milky latex fluid exudes. This fluid contains esters that irritate the skin if touched. Leaves are the site of photosynthesis in plants, the process by which light energy is converted into chemical energy stored in sugars. The green colour is due to chlorophyll.