Diversity of the slippery zone microstructure in pitchers of nine carnivorous Nepenthes taxa

Using a cryo-scanning electron microscope, we studied microstructure of the slippery zone in nine Nepenthes taxa. For N. fusca, N. macrophylla, N. mirabilis, N. ventricosa, N. dicksoniana, and N. veitchii, it was examined here for the first time. Three types of the slippery zone were distinguished among the studied taxa: (1) with well-developed crystalline wax coverage, (2) with greatly reduced wax coverage, and (3) without wax crystals. These data were combined with morphometrical measurements of the two pitcher zones primarily relevant to prey catching and retaining: the slippery zone and the peristome. In species with fully developed wax coverage, the slippery zone was longer and the peristome was narrower compared to those with reduced or lacking crystalline wax. We found statistically significant negative correlation between the relative length of the slippery zone and the relative width of the peristome. Based on the analysis of the relationship between the microstructure of the slippery zone and pitcher macromorphology, two main types of pitchers in Nepenthes are proposed: (a) traps based predominantly on the waxy slippery zone and (b) peristome-based traps.