In defence of the entity of Macaronesia as a biogeographical region

Abstract

Since its coinage ca. 1850 AD by Philip Barker Webb, the biogeographical region of Macaronesia, consisting of theNorth Atlantic volcanic archipelagos of the Azores, Madeira with the tiny Selvagens, the Canaries and Cabo Verde, andfor some authors different continental coastal strips, has been under dispute. Herein, after a brief introduction on the termi-nology and purpose of regionalism, we recover the origins of the Macaronesia name, concept and geographical adscription,as well as its biogeographical implications and how different authors have positioned themselves, using distinct terrestrial ormarine floristic and/or faunistic taxa distributions and relationships for accepting or rejecting the existence of this biogeographical region. Four main issues related to Macaronesia are thoroughly discussed: (i) its independence from theMediterranean phytogeographical region; (ii) discrepancies according to different taxa analysed; (iii) its geographical limitsand the role of the continental enclave(s), and, (iv) the validity of the phytogeographical region level. We conclude that Macaro-nesia has its own identity and a sound phytogeographical foundation, and that this is mainly based on three different floristic com-ponents that are shared by the Macaronesian core (Madeira and the Canaries) and the outermost archipelagos (Azores and CaboVerde). These floristic components are: (i) the Palaeotropical-Tethyan Geoflora, formerly much more widely distributed inEurope and North Africa and currently restricted to the three northern archipelagos (the Azores, Madeira and the Canaries);(ii) the African Rand Flora, still extant in the coastal margins of Africa and Arabia, and present in the southern archipelagos(Madeira, the Canaries and Cabo Verde), and (iii) the Macaronesian neoendemic floristic component, represented in all thearchipelagos, a result of allopatric diversification promoted by isolation of Mediterranean ancestors that manage to colonizeCentral Macaronesia and, from there, the outer archipelagos. Finally, a differentiating floristic component recently colonizedthe different archipelagos from the nearest continental coast, providing them with different biogeographic flavours.