Ex situ plant collections established from seeds of natural populations are key tools for understanding mating systems of intricate taxonomic complexes, as in the Limonium Mill. genus (sea lavenders, Plumbaginaceae). Plants show a polymorphic sexual system associated to flower polymorphisms such as ancillary pollen and stigma and/or heterostyly that prevents self and intramorph mating. The main objectives of this study were to investigate the significance of pollen-stigma dimorphisms and the role of flower visitors in the reproductive output of hybrids arising from sexual diploids of Limonium ovalifolium complex and apomicts tetraploids of L. binervosum complex in an open cross-pollination experiment. Results showed that, similarly to parental plants, hybrids present inflorescence types, self-incompatible flowers, and produced regular pollen grains with the typical exine patterns, with medium to high viability. By contrast, apomicts show floral polymorphisms, inflorescences, and pollen grains of maternal phenotype but with low stainability. Several insects' species visited the inflorescences of parental plants and both hybrids and apomicts and some of these insects carried A and/or B pollen grains on their bodies, especially Clepsis coriacana (Rebel) and Tapinoma sp. Insects' floral visits to hybrids and apomicts seem to be independent of pollen fertility and plants' reproductive modes. Both hybrids and apomicts were able to produce fertile seeds, although the latter showed more seedlings with developmental anomalies than the first plants. The findings demonstrate that there is a weak reproductive barrier between the diploid species of L. ovalifolium complex as they can hybridize and produce fertile hybrids, provided there is pollen transport by pollinator insects. This study supports that apomixis is a strong reproductive barrier between both L. ovalifolium and L. binervosum complexes but did not allow us to exclude reproductive interferences of apomict pollen into sexuals.
Keywords: ancillary pollen and stigma polymorphisms; apomixis; flower heteromorphism; pleiocotyly; polyembryony; polyploidy; reproduction.