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Reintroduction of native species has become increasingly important in conservation worldwide for recovery of rare species and restoration purposes. However, few studies have reported the outcome of reintroduction efforts in plant species. Using data from the literature combined with a questionnaire survey, this paper analyses 249 plant species reintroductions worldwide by assessing the methods used and the results obtained from these reintroduction experiments. The objectives were: (1) to examine how successful plant species reintroductions have been so far in establishing or significantly augmenting viable, self-sustaining populations in nature; (2) to determine the conditions under which we might expect plant species reintroductions to be most successful; (3) to make the results of this survey available for future plant reintroduction trials. Results indicate that survival, flowering and fruiting rates of reintroduced plants are generally quite low (on average 52%, 19% and 16%, respectively). Furthermore, our results show a success rate decline in individual experiments with time. Survival rates reported in the literature are also much higher (78% on average) than those mentioned by survey participants (33% on average). We identified various parameters that positively influence plant reintroduction outcomes, e.g., working in protected sites, using seedlings, increasing the number of reintroduced individuals, mixing material from diverse populations, using transplants from stable source populations, site preparation or management effort and knowledge of the genetic variation of the target species. This study also revealed shortcomings of common experimental designs that greatly limit the interpretation of plant reintroduction studies: (1) insufficient monitoring following reintroduction (usually ceasing after four years); (2) inadequate documentation, which is especially acute for reintroductions that are regarded as failures; (3) lack of understanding of the underlying reasons for decline in existing plant populations; (4) overly optimistic evaluation of success based on short-term results; and (5) poorly defined success criteria for reintroduction projects. We therefore conclude that the value of plant reintroductions as a conservation tool could be improved by: (1) an increased focus on species biology; (2) using a higher number of transplants (preferring seedlings rather than seeds); (3) taking better account of seed production and recruitment when assessing the success of reintroductions; (4) a consistent long-term monitoring after reintroduction.

The increased demand of food produced through sustainable agriculture has resulted in localised amelioration of intensive management imposed by agroecosystems. However, these newly available niches are often isolated and plant species may not be able to recolonise fragmented agroecosystems from where they have been extirpated. Plant reintroduction can overcome dispersal limitation in agroecosystems but may also generate conflicts that jeopardise conservation efforts. Conflicts arise when reintroductions are perceived to place constraints on the management and productivity of agroecosystems: the translocated plants may require space sharing with crops, may have negative effects on crop yields, and come with the expectation that farmers must modify their farming practices and accommodate legal obligations deriving from protected species status. Benefits include economic incentives that pay farmers through CAP, the conservation of nature, ecosystem services, an effective marketing strategy and increased aesthetic value that might generate ecotourism.\ud \ud We discuss the practical implications of the abovementioned issues by reference to two cases of European species in which different approaches to reintroduction resulted in opposite outcomes (i.e., consensus vs. opposition). Coexistence of threatened plants and crops is possible if farmers and local stakeholders are involved in a conservation project from an early stage and if farmers conservation efforts turn into benefits for their income. Based on these considerations, we propose a strategic framework to promote reintroduction of threatened plants in agroecosystems (land sharing) and policy advancement aimed at recognising the role of farmers in maintaining biodiversity on their lands.

Marsilea quadrifolia L. is a leptosporangiate aquatic fern which has a played key role in the evolutionary history of plants. It is characterized by heterospory, the ancestral progressive trait that led to the evolution of seeds. The species has creeping, fleshy, adventitious roots containing multiple rhizomes. From the rhizomes a four-leaf clover grows above the water level with a long petiole, at the base of which the sporocarps containing spores are located. Its life cycle is characterized by alternation of generations; reproduction occurs either sexually or by vegetative propagation. The species grows in wet habitats containing shallow water. In the natural environment this includes lakes and small rivers; in agricultural areas it can be found in ditches and rice fields. The species can tolerate nutrient rich waters and because of its phytoremediation properties is capable of partially counteracting the negative effects induced by a moderate organic enrichment of sediments. It has been harvested for centuries in Asian countries as both a food source and for ethnobotanical use in Ayurvedic medicine. Supposed medicinal properties include antibacterial, diuretic, depurative, cytotoxic and antioxidant effects, but these require further investigation and testing. M. quadrifolia has a widespread distribution, occurring throughout central-southern Europe and extending from Eurasia to tropical and temperate areas of eastern Asia and North America, where it is considered a non-native species. Despite its wide distribution, in its home range the species is threatened with extinction and has already been locally extirpated in several European countries. As a result, it is listed as “Vulnerable” in the European Union Red List due to its scattered distribution and declining population. Habitat loss and degradation, excessive water eutrophication, and agricultural practices such as the use of herbicides, mechanization and simplified rotation are the main threats to the species. As it is listed in Appendix I of the Bern Convention and in Annexes II and IV of Directive 92/43/EEC as a strictly protected species, in situ and ex situ conservation activities have been conducted in most European countries. Reintroduction, cultivation in botanical gardens and in vitro propagation are the most commonly applied conservation methods.