The scientific name for oaks, Quercus, is derived from two Celtic words: - quer meaning fine, and cuez meaning tree. Oaks are indeed fine trees. Branched and spreading, mature trees create an immense crown area. The oaks are unique in producing acorns for fruit. Their catkins (or flower groups) can be either male or female, with both sexes present on the same tree. They rely on the wind to assist in pollination. Oaks have extremely variable foliage, even on the same tree. Each species of tree can hybridize (interbreed) with other species, adding to this effect. This variation can make identification difficult. At Pinnacles, three tree species—valley oak, blue oak and coast live oak —stand out.