Organogenesis of the Inflorescence and Flowers in Platycarya strobilacea (Juglandaceae)

Abstract

The reproductive structures of the monotypic genus Platycarya (Juglandaceae), in particular the nature of the fruit wings, have been interpreted variously. We investigated organogenesis of inflorescence and flowers with scanning electron microscopy (SEM). This is the first SEM study to show the whole developmental process of male, female, and bisexual flowers in a member of the Fagales. In staminate and bisexual flowers, only a subtending bract is present, while bracteole and perianth are absent. Four to 10 stamen primordia of different sizes are arranged as an irregular circle or two semicircles. With further development of the stamens, the receptacle, which is fused to the base of the bract, enlarges, and the whorled arrangement of stamens becomes less and less distinct. In pistillate flowers, the transversely ellipsoidal floral primordium develops a central depression. Two bracteoles are initiated in the lateral position of the floral primordium. Soon, the inconspicuous circular perianth primordium appears around the central depression, and two carpels are initiated bordering the central depression opposite to the bracteoles. The perianth is highly reduced and fused with the ovary wall from the initial stage. Each wing of the fruit of Platycarya strobilacea is formed by a combination of one bracteole and the lateral lobe of the perianth.