An umbel of milkweed flowers. In addition to reflexed calyx and corolla lobes, the unique flower of milkweed features a crown, a structure formed by five petaliferous corolla appendages. These are hooded. Each may have an additional outgrowth called horn. In clasping milkweed the crown is pink. Stamen filaments are united in a tube enclosing the style. Anthers are also united with each other and the stigma forming a stigmatic disk. The surface that receives the pollen is hidden on the lower side of the disk, covered by the united anthers.