There 5 sepals and 5 petals in this male flower of Acer platanoides, Norway maple. In the center of the flower is a large green nectar disk to attract insect pollinators. Note that there are 8 (eight!) stamens, a common number in the Aceraceae. There is NO rudimentary gynoecium.
Photo by K. R. Robertson and D. L. Nickrent of plants growing in Champaign, Illinois.