Relationship between trap anatomy and function in Australian carnivorous bladderworts (Utricularia) of the subgenus Polypompholyx

• The trap wall anatomy was studied in nine Australian Utricularia species.
• The walls of all Utricularia traps studied consisted of two to five cell layers.
• Lag-period of water pumping occurs in Utricularia dichotoma traps just after water aspiration.
• The number of cell layers in the trap wall is not decisive for the trap firing–resetting rate.

The suction traps of carnivorous Utricularia species are hollow bladders of foliar origin which trap and digest small organisms. In this paper, the trap wall anatomy and thickness in nine Australian Utricularia species belonging to three generic sections (Pleiochasia, Polypompholyx, Tridentaria) within the subgen. Polypompholyx are described. It is hypothesized that there is a close relationship between Utricularia trap wall anatomy and functional trap characteristics – species with more than two cell layers in their trap walls are less effective at trap firing (i.e., water aspiration) and resetting (water pumping) than species with two-layered trap walls. The trap walls of all Utricularia species studied using light microscopy consisted of two to five cell layers. A distinct variation in the trap wall structure occurred not only within one generic Utricularia section, but even within one species and also different parts of one trap. Using an electronic position sensor to monitor trap thickness showed that in two clones of Utricularia dichotoma, both firing (41 ± 2 and 46 ± 3 μm mm−1) and resetting rates per unit trap length (14 ± 1 μm mm−1 per 30 min) were markedly lower than the mean values for 13 aquatic Utricularia species obtained from the literature (73 ± 2 and 52 ± 2 μm mm−1, respectively). In conclusion, the number of cell layers in the trap wall may not in itself be decisive for the trap firing–resetting efficiency. The lag-period of water pumping by the trap, which can be caused by a different regulation mechanism of water pumping, is probably confined to the species from the Pleiochasia section in contrast to the aquatic species from the Utricularia section.