ACER, in botany, the maple or sycamore tree, a genus of the polygamia dioecia class. There are ten species of this genus. The calix of the female is quinquefide, the corolla pentapetalous, the stamens eight, one pistil, and two seed-capsules. The calix of the male is also quinquefide, the corolla pentapetalous, and the stamens eight. There are only two species of the acer which are reckoned natives of England, viz. the pseudo-platanus, and the campestre.