Why some groups of species radiate, when others appear not to have done so, remains a fundamental question in evolutionary biology. Here, we investigate why island endemism, a common surrogate of speciation rate, reaches its lowest levels among land plants in bryophytes. Using molecular phylogeographical analyses in the moss genus Rhynchostegiella, we contrast the hypotheses (1) that the small size of oceanic islands and moderate genetic isolation in island populations with high dispersal capacities promote lower anagenetic diversification rates than in continental populations, and (2) that island and continental speciation rates do not differ, but island endemics quickly colonize continents.

Macaronesia, Europe and Africa.

A time-calibrated multilocus species tree for 80 populations, representing the nine species of Rhynchostegiella across their entire distribution range, was constructed using beast. Based on this dated tree, ancestral ranges were estimated in biogeobears and speciation rates using bamm.

Although island-endemic Rhynchostegiella species evolved anagenetically, speciation rates did not significantly differ between island and continental lineages. Seven episodes of colonization from islands to continental regions were inferred from ancestral-area estimations, which identified the Canary Islands as the ancestral distribution area of the genus, lending support to our second hypothesis.

Our findings reinforce the view of north-eastern Atlantic archipelagos as ‘departure gates’ for the colonization of western Europe during the late Pleistocene. They further show that, over longer evolutionary time-scales, the colonization of continents from island ancestors can lead to speciation and contribute to extant patterns of continental diversity.