The Macaronesian region comprises the volcanic, oceanic archipelagos of the Cape Verdes, the Canaries, the Savage or Selvagem Islands, Madeira and the Azores, located in the Atlantic Ocean between 15 and 30°N (Fig. 14.1). In keeping with other volcanic oceanic archipelagos, Macaronesia is characterised by high levels of endemicity and recent years have seen the rapid development of novel hypotheses to explain aspects of the evolution of diversity in the region. The availability of checklists for the biota for each of the Macaronesian archipelagos (Izquierdo et al., 2004; Arechavaleta et al., 2005; Borges et al., 2005a, 2008) has led to the development of new hypotheses to explain diversity patterns in the flora in relation to abiotic factors (Emerson & Kolm, 2005; Whittaker et al., 2007, 2008; Borges & Hortal, 2009). Silvertown (2004; see also Silvertown et al., 2005; and for other views, Herben et al., 2005; Saunders & Gibson, 2005) reviewed the results of phylogenetic analyses and suggested that ‘niche pre-emption’ may explain the radiation of some groups but not others. Carine et al. (2010) also used phylogenetic data to demonstrate that angiosperm groups which showed island woodiness (i.e. the evolution of woodiness linked to the colonisation of islands) were typically more species-rich than groups with the same habit on both continent and islands and hypothesised that the evolution of woodiness promoted diversification. Data from checklists together with phylogenetic information led Carine and Schaefer (2010) to suggest that differences in the climatic histories of the Canaries and Azores may explain the marked differences observed in patterns of endemicity in the angiosperm floras of the two archipelagos.