Micromorphology and anatomy of fruit in Iris pseudacorus L.

Abstract

Based on the suggestion that flower and fruit are integrally evolving structures, we aimed to reveal the floral traits persisting in the fruit structure in Iris pseudacorus, a widely distributed riparian species in Ukraine. We intended to compare the results with the other Iris species studied previously and reveal the constancy of micromorphological features of fruit interior structure. We revealed exomorphological and micromorphological peculiarities of the fruiting ovary using the model of vertical zonality of the gynoecium, vascular anatomy, and general anatomy of the fruit wall. In the fruiting ovary of I. pseudacorus, we revealed the presence of three vertical zones: short synascidiate zone, long symplicate zone bearing uniseriate seeds, and hemisymplicate zone located in the fruit beak. The vascular system of the ovary is composed of dorsal, septal, and ventral veins. Each of three dorsal veins divides radially into the outer tepal trace, stamen trace, and dorsal carpellary bundle, while each septal vein divides tangentially into three bundles of the inner tepal trace. Paired ventral veins enter the ovary from its bottom and supply ovules and seeds. The exocarp is composed of polygonal cells with thickened cellulose walls. The endocarp is uniseriate, unlignified, and composed of live prosenchymal cells, which are elongated tangentially. In the parenchymatous mesocarp, a great number of secretory canals with tannin-like content occur. The dehiscence of fruit on three valves proceeded by both dorsal and ventral slits. Dorsal slits are formed along dorsal grooves and provided by small-celled tissue surrounding the dorsal veins. The presence of ventral sutures of carpels in the symplicate zone of the ovary provides ventral dehiscence of fruit. Hence, the structure of the fruiting ovary in I. pseudacorus is comparable to that of other Iris species. Our investigation confirmed that the vertical zonality, placentation, and vascular system of the gynoecium in Iris can be appropriately estimated in the fruiting stage because the structural components of the ovary, which developed at the pre-anthetic phase, persist in the fruit.