Quantitative morphologic-anatomical analysis of inner trap structures of Genlisea hispidula

Premise: Among the sophisticated trap types in carnivorous plants, the underground eel-traps of corkskrew plants (Genlisea spp., Lentibulariaceae) are probably the least understood in terms of their functional principle. Here, we provide a detailed analysis of structural and hydraulic features of G. hispidula traps, contributing to the ongoing debate on whether these traps can actively generate water streams to promote prey capture. Methods: Anatomical and hydraulic traits were investigated quantitatively on detached traps, including inner trap diameters, chamber line element, hair length, glandular pattern, and hydraulic conductivity. These measurements were based on light and electron microscopy, X-ray microtomography, and hydraulic measurements. Key results: Hydraulic resistivity in the neck of the trap, from the trap mouth towards the vesicle (digestive chamber) was ten times lower than in the opposite direction. The comparison of measured and theoretical flow rates suggests that the retrorse hairs inside trap necks provide also considerable resistance against movement of matter towards the vesicle. Hair length showed a gradient along the neck, with the shortest hairs present near the vesicle. Co-occurrence of quadrifid and bifid glands was limited to a small part of the neck, with quadrifids occurring near the vesicle, and bifids towards the trap mouth. Conclusion: The combination of structural gradients with hydraulic anisotropy suggests the trap to be a highly fine-tuned system based on likely trade-offs between efficient prey movement in the trap interior towards the vesicle, prey retention, and spatial digestion capacities, and also does not argue against the generation of water streams.