Key ecological determinants of the reproductive success and conservation strategy of Delphinium pentagynum subsp. formenteranum ( Ranunculaceae ), an endangered endemic species of the western Mediterranean Basin (Balearic Islands)

Delphinium pentagynum subsp. formenteranum is an endemic species restricted to the island of Formentera (Balearic Islands), where it is considered an endangered species. Ecological traits such as pollination and pollinator-plant interaction, and seed germination are key processes required for conservation efforts but remain poorly characterized. Floral traits were evaluated analysing total alkaloid content for vegetative plant, floral, nectar and pollen, and volatile emitted by flowers. Flowering phenology was assessed in the field in three different years (1998, 2008, 2018) and under cultivated conditions for D. pentagynum subsp. formenteranum and cohabiting species. Germination trials were conducted both at different constant and alternate temperatures, and seed lots conserved at room temperature were germinated across 7 years to assess seed viability with seed age. Micromorphological seed traits were assessed with scanning electron microscopy. Results show intraspecific flowering synchrony for D. pentagynum subsp. formenteranum with flowering occurring in May after the flowering peak of cohabiting species. Floral traits show lack of odor related volatiles and high alkaloid content in plant and flowers. Germination remains unaffected within a broad spectrum of temperatures and is only negatively affected at high temperatures (23ºC). Seed viability maintains high germination rates for the first 2 years (~ 100%) and decreases after four-five years (40–60%) and six years (20%), being non-viable after seven years. Both phenological displacement and alkaloid content in flowers support pollination specificity, which is restricted almost exclusively to Anthophora balearica. Germination ecology is dependent mainly on water availability, but high seed longevity allows probable transient bank seed.