in botany, a genus of the monocotyledon polyandria class. The calyx of the male has five segments; it has no corolla; and the stamens are from five to ten. The calyx of the female is one entire, rough leaf; it has no corolla; the styli are from two to five; and the seed is ovate. There are 14 species, only one of them, viz. the robur, or common oak, a native of Britain.