Comparative Micromorphology and Anatomy of Crested Sepals inIris(Iridaceae)

Abstract

Premise of research. The Iris flower is considered to be a pseudoinflorescence by having three pollination units, each acting as a labiate flower. The sepal provides the entrance, “floor,” and “walls” of the pollination tunnel and is sometimes adaxially elaborated with various structures, such as ridges, crests, and protuberances. Crested sepals have a prominent median crest that lies along the proximal-distal axis of the pollination tunnel and sometimes also have various lateral structures on the entrance, floor, or walls of the pollination tunnel, suggesting that they may play a role in pollination. Crested sepals are morphologically diverse and have evolved at least five times in Iris. Understanding their micromorphology and anatomy will shed light on the diversification of perianth and provide insights into flower-pollinator interaction.Methodology. Micromorphologies of the adaxial epidermis and anatomical characteristics of selected crested sepals representing different patterns of structural elaborations as well as ridged and nonelaborated sepals were studied using scanning electron microscopy and light microscopy.Pivotal results. Compared with nonelaborated sepals, the occurrence of the median and sometimes lateral structures on crested sepals changes not only the architecture of the pollination tunnel and its entrance but also the epidermal topology within the pollination tunnel by creating new epidermal zones. Compared with ridged sepals, crested sepals have a more sophisticated median structure that is usually more prominent and elaborated at the pollinator entrance and/or the distal half of the pollination tunnel. Vascular tissues and trichomes are also present in or on some of the median and lateral structures.Conclusions. The micromorphologies and anatomical features of crested sepals are diverse even though convergences in terms of epidermal topology and the occurrence of vascular tissues in elaborate structures also occur among independently evolved crested lineages in Iris. Structural elaborations may provide optical and tactile cues or stimuli to pollinators.