Re-introduction of the four leaf clover in the agricultural context of the Po River Plain, Italy

Summary

The four leaf clover fern (Marsilea quadrifolia), Vulnerable in Europe and Endangered in Italy, has disappeared from southern Italy through herbicide use in rice cultivation, competition from invasive plants, and predation by non-native Louisiana crayfish and nutria. Between 2010 and 2012, researchers from the University of Pavia and Milano-Bicocca ran three linked projects to reintroduce the fern across the Po River Plain within Natura 2000 protected areas, since low genetic diversity meant source-population choice was not a major concern but raised the risk of inbreeding depression. Small rhizome portions were collected from two relict northern Italian populations and vegetatively propagated over two years, since in-vitro spore crossing proved very difficult; each release site was structured as a meta-population of several sub-populations to buffer against local losses, including at Bagnacavallo, where a pond was excavated to exclude crayfish and control water flow, and artificial floating islands were used at a site with high water-level fluctuation. Herbicide tolerance testing showed the fern was highly sensitive to common rice-field chemicals, restricting release sites to areas with minimal agricultural impact. Monitoring found cover doubled within six months of planting but fell to 50% the following year, reflecting sensitivity to fluctuating water levels and rainfall; some sub-populations died out within three years from poor microsite choice or predation, though the meta-population structure limited overall damage, and at Bagnacavallo only the artificial pond population has persisted. The project rates itself successful, citing thorough threat analysis, ecological understanding from long-term study of wild populations, herbicide-tolerance data guiding site selection, and the fern's capacity for rapid vegetative growth.