More than 50 % of the German land area is used for agriculture. The rapid modernisation of fieldwork (denser seed spacing, usage of herbicides and pesticides, deeper digging, fertiliser usage, lower ground-water table, etc.) has contributed to a massive change in the German cultural landscape, which results in biodiversity loss. Apart from these indirect effects, direct reductions in biodiversity by removing field weeds have contributed to this loss. These massive changes promoted more abundant plant species that perform better in a wider range of abiotic factors than rare plant species, which have difficulties surviving in such landscapes. However, not only plants suffer from the consequences of today’s cultivated landscape but also insects. To combat biodiversity loss, flower strips and meadows have been used to support plant and insect biodiversity. However, high-quality seed mixtures are also expensive. More cost-saving seed mixtures are available for creating flowering meadows, but their effectiveness is significantly lower. The flowering strip dilemma refers to the challenge of determining the optimal time to plow up flowering strips to enhance species richness because older flowering strips exhibit reduced flowering activity and increased grass dominance. The EU-Interreg-funded project ExpBio (https://www.interregnorthsea.eu/expbio) attempts to tackle the loss of plant and insect biodiversity from the perspective of regionally adapted seed mixtures. These seed mixtures will be sown to answer multiple questions: How do German regionally adapted seed mixtures perform compared to Dutch and Swedish regional seed mixtures? Do local pollinators prefer regional plants? Do regionally adapted seed mixtures increase insect biodiversity more than non‑regional seed mixtures? To test these hypotheses, regional and non-regional seed mixtures were sown, and parameters such as pollen ratio, nectar content, pollen viability, seed viability, grass species invasion and species richness will be assessed.

Achillea millefolium L. and Campanula rotundifolia L. occur in most seed mixtures. Genetic investigations revealed that the population structure of these plants did not match the areas of origin of the regional seed mixtures in Germany. Do we even need these areas of origin or would it be possible to exchange genotypes that are found in one place to another place without worrying? To address this question, samples from our European neighbours will be analysed, and the genetic similarity will be determined. Another question is whether wild plants from different seed mixtures differ in their pollen and nectar contents. Furthermore, is there a difference between the pollen and nectar content of wild and cultivated plants?

In addition, a forgotten group of field weeds will be examined. The members of the Lilium bulbiferum group are L. croceum Chaix, L. bulbiferum L., and L. buchenavii Focke ex R.J.Koch. The difference among these three taxa lies in their vegetative reproduction methods. Lilium croceum vegetative reproduces only via underground stolons, L. bulbiferum reproduces via aerial bulbils along the stem, and L. buchenavii reproduces via bulbils only on inflorescences. Generative reproductive methods differ. For example, L. buchenavii, which is known only from a single clone, cannot reproduce by seeds because of self‑incompatibility. Changes in the reproductive system can significantly affect how a species thrives and lead to diversification. Morphological and reproductive system data are crucial to distinguish between species. Nevertheless, in the post-genomic era, genomic data are required for plant taxonomy to support differentiation between species.

After exploring the systematics and population genetics of the L. bulbiferum group, the implementation of members of this group in flowering meadows will be evaluated. In Germany, it is unknown whether pollinators visit flowering lilies or whether insects are pollinators. It is also unknown how lilies cope with freshly seeded flowering meadows. However, individuals have been observed on fallow lands and meadows, which appear to be very site-loyal once they have established themselves.