Floral traits and reproductive success variation among inflorescence orders in Eryngium maritimum

Abstract

Eryngium maritimum L. is considered a key species in dunes of the western Mediterranean. Although Northern European populations are endangered, the Mediterranean populations show a good conservation status, despite a lack of studies of the reproductive requirements and strategies of this species. This study aims to analyse the reproductive biology of a population of E. maritimum in the western Mediterranean (Balearic Islands, Spain), specifically focusing on differences in morphometric and reproductive traits among inflorescence orders. Capitulum size, number of flowers, fruit set and seed set were analysed to evaluate the morphological and reproductive differences among inflorescence orders. The association between subterranean development and investment in reproductive structures was also studied along the dune location. Breeding system was analysed, evaluating self-pollination capacity at capitulum level and the pollen/ovary ratio. Finally, floral visitors were assessed. Morphometric and reproductive traits showed a decline in size and production from early to subsequent inflorescence orders. A correlation between width of stem base (caudex) and number of reproductive structures was observed, whereas seashore distance did not affect the reproductive development. Flowering occurred during summer, from May until late July, while fructification took place from the middle of August until the last days of September. Pollinator exclusion treatments induced a fruit and seed set decline. Twenty-one species of floral visitor were found. First and second inflorescence orders contributed to the generation of seeds, displaying high fruit and seed production, while other inflorescence orders seemed to attract pollinators. Reproductive and non-reproductive development could depend on the capacity to reallocate resources from underground to aerial structures, which seemed to be superior in samples with highly developed caudices. In the studied population, inner areas closest to the seashore showed a delay in anthesis, which could be related to microclimate differences along the coast-to-inland gradient. Pollination is strongly entomophilous and showed low levels of self-compatibility at capitulum level. Considering these results, for habitat conservation the reported microclimate diversity should be taken into consideration, with a focus on conservation of the pollinator populations.