Seed reproductive biology of the rare aquatic carnivorous plant Aldrovanda vesiculosa (Droseraceae)

Abstract

© 2016 The Linnean Society of London. Despite the unprecedented global decline in extant populations of Aldrovanda vesiculosa in the last century, little is known about the reproductive biology of this iconic aquatic carnivorous plant. This study aimed to investigate the role of seed-based reproduction in the ecology of A. vesiculosa, with particular focus on the interplay between the regulation of seed dormancy by temperature cues and the efficacy of exogenous ethylene gas to act as a germination stimulant, the desiccation capacity and long-term storage potential of seeds for conservation purposes. Sexual reproduction appears to be extremely limited in both natural and naturalized populations across three continents, with high variability in the success of flowering and seed set between sites and between seasons. Overall, flowering yielded few fertile fruit (6-19% of flowers producing fertile fruit) and seed viability was variable but generally low (29-88%). Fecundity appears to be influenced by seasonal climatic conditions and microhabitat characteristics. Aldrovanda vesiculosa possesses physiologically dormant seeds, with germination stimulated by exposure to ethylene gas (>90% germination) at 25 °C. Seeds appear sensitive to desiccation and sub-zero temperature storage, with no germination and markedly reduced embryo growth after storage of seeds for >1 month at 15 °C and 15% relative humidity or after short-term (24 h) storage at -18 °C. In the absence of significant conservation and restoration initiatives, the continuing decline of dystrophic freshwater wetland habitats globally leaves A. vesiculosa facing extinction. As the successful long-term storage of seeds appears unfeasible based on the approaches described in this study, other alternatives for germplasm conservation such as cryostorage of vegetative tissues or zygotic embryos must be considered for establishing long-term ex situ collections of critical germplasm.