Living between land and water - structural and functional adaptations in vegetative organs of bladderworts

Abstract

Aims The carnivorous Utricularia (Lentibulariaceae) has an anatomically simple and seemingly rootless vegetative body. It occupies a variety of wetlands and inland waters and shows a broad range of life forms. Here, we aimed to elucidate structural and functional traits in various hydric conditions. Furthermore, we intended to evaluate morpho-anatomical adaptations in correlation with life forms. Methods Morpho-anatomical characteristics typical for hydrophytes of all life forms were investigated by light microscopy on 13 Utricularia taxa, compared to one Pinguicula and two Genlisea taxa, and assessed by multivariate analyses. Results Vegetative structures of Utricularia and Genlisea showed reduced cortical, supporting, and vascular tissues. With increasing water table, leaves were thinner, and narrower or dissected, and submerged organs tended to contain chloroplasts in parenchymatic and epidermal cells. In some main stolons, an endodermis with Casparian strips was visible. Large gas chambers, including a novel 'crescent' and a special 'hollow' aerenchyma pattern, were found in amphibious to free-floating taxa. Conclusions The evolutionary transfer of carnivory from aerial to subterranean organs in Genlisea, and even more in Utricularia, coincides with a highly simplified anatomy, which is adapted to a broad variety of hydric conditions and compensates for structural innovations in the uptake of nutrients.