The pollen fertility of F₁ hybrids, ranging from progeny within natural populations to synthetic hybrids between species of Tolpis from three archipelagos in Macaronesia, was determined. Pollen fertility of F₁ hybrids of inter-archipelago crosses from the Azores, Canaries, and Madeira were generally lower than crosses between populations or species in the same archipelagos. Lower pollen fertility was pronounced in hybrids between plants from the Canaries and the other archipelagos, which is concordant with a more distant phylogenetic relationship between the Canaries, and the Azores and Madeira. Lower average pollen fertility was seen between plants from different as compared to the same clades in the Canary Islands. However, low pollen fertilities were also detected between plants from some populations/species in the same archipelagos, and even among progeny of individual maternal plants. Some hybrids with reduced fertility had meiotic irregularities, suggesting chromosomal rearrangements; in other cases meiosis appeared normal. Results indicate that postzygotic isolating factors evolved subsequent to the divergence of Tolpis in the three archipelagos, but there are hybrid sterility factors among plants within each of the archipelagos, and even within some natural populations. Phylogenetic relationships in the Canary Islands indicate that divergence has occurred within the last million years. Present results implicate postzygotic factors as reproductive barriers facilitating population divergence and speciation in Macaronesian Tolpis.