Reproductive biology and reproductive output assessment in natural and introduced subpopulations of Apium bermejoi,a ‘Critically Endangered’ endemic plant from Menorca (western Mediterranean)

Apium bermejoi is a critically endangered species that is native to Menorca, an island of 702 km² located in the western Mediterranean basin. We investigated the reproductive biology of this species and evaluated flowering/fruiting phenology and reproductive output in wild subpopulations over four years (2007–2010). We used ex situ cultivated plants to study floral biology and performed bagging experiments to elucidate the breeding system. We addressed the role of ants in seed dispersal/predation in wild subpopulations by analysing the presence of A. bermejoi seeds in the waste accumulated on the refuse piles of all anthills. Our observations indicated that flowers are protandrous but that there is no dichogamy between flowers within and among umbels of the same individual. Moreover, individuals are mixed in the field because the close germination of several seeds and the plant’s caespitose habit promote cross‐pollination. Bagging experiments demonstrated that the species is autogamous, and seeds from selfing (bagged with muslin) showed high final germination (>80%). However, the fruit set of selfed umbels (0.3–0.4 per 1) was lower than that of open‐pollinated umbels (0.6–0.8 per 1), and the high pollen/ovule (P/O) ratio (3641±133, n= 30) was also indicative of xenogamy. Plants bagged with muslin, bagged with tulle or barred from contact from ants exhibited similar fruit sets, lower than those observed in isolated and control groups, suggesting that anemophily and pollination by flying insects were less effective than ant‐based pollination. We identified eight species of floral visitors, and we noted that ants were the most frequent visitors. Although we found some A. bermejoi seeds in the refuse piles of Messor bouvieri anthills, most of the seeds were not damaged (99.1%), and the number of seeds found represents only a small proportion of the overall fruit production. Because sexual reproduction is the main reproductive mechanism of these plants, despite their high potential for space colonisation and vegetative propagation, the reproductive output for each year determines the subpopulation configuration in the following year.