Comparative anatomy of the gynoecia of Iris species (Iridaceae) with different degrees of longitudinal fusion of the carpels

The gynoecia of Iris exhibit three different degrees of longitudinal fusion of the carpels. Most species, including Iris pallida Lam., have a very short stylar tube and three long tangentially flattened and broadened style branches. Iris domestica (L.) Goldblatt & Mabb. is the only species that has a very long stylar tube and three extremely reduced style branches. In three other species, including Iris dichotoma Pall., both the stylar tube and style branches are well developed, with the stylar tube occupying approximately one-third to half of the length of the style. Anatomical characteristics are compared for the gynoecia of these three species using serial transverse sections and light microscopy. Except the stylar crest, homologous regions of the main body of the carpel (MBC), stylar wings, stylar flaps, and stylar canals were found in the stylar tube and style branches of all three species. A conserved pattern of vascular distribution was found in the stylar tube and ovary, and vascular tissues were only found in the MBC of all three species. The style branches of these three species differ in terms of quantity and location of vascular branching. This study indicated that heterotopic development of the stylar tube and style branches may contribute to the evolution of three different types of gynoecia in Iris.