Reproductive biology insights for the conservation of Euphorbia fontqueriana, a rare endangered plant species from the western Mediterranean Basin

This study focuses on the reproductive biology of Euphorbia fontqueriana, an endangered species endemic to Mallorca (western Mediterranean Basin). Individuals were monitored weekly to assess flowering and fruiting phenology, flowering synchrony, cyathium gender, and reproductive output in two consecutive years. Hand-pollination treatments were performed to test for autonomous self-pollination, anemogamy and pollen limitation. In vitro germination tests were performed to test for photoinhibition and dormancy, and in situ seedling recruitment was monitored. Results showed that the species exhibits functional androdioecy (male and hermaphrodite plants) overlapping functional andromonoecy (male and hermaphrodite cyathia in hermaphrodite plants). Hermaphrodite plants showed a low degree of anthesis overlap among inflorescence levels, but a high overlap between both phases within cyathia that do not prevent from geitonogamy. Euphorbia fontqueriana bloomed during a few weeks and insects were required for pollination. In natural conditions, fruit set was similar to 60%, but we did not find evidence of pollen limitation. Most of the reproductive individuals consist of one flowering branch producing similar to 5 seeds. Seeds showed photoinhibition and dormancy, and seedling recruitment was very low. Overall, this study contributes to acquire knowledge of the floral biology and pollination ecology of this endangered range-restricted species, which is discussed under a conservation context.