Beyond Cladistics: The Branching of a Paradigm

7. Endemism and Evolution of the Macaronesian Flora

101 SEVEN Ma r k A. Carine, Ar noldo Santos-Guer ra, I. R o sa n a G uma, and J. Alfredo Reyes-Betancor t ENDEMISM AND EVOLUTION OF THE MACARONESIAN FLORA The Macaronesian region (Fig. 7.1) comprises the volcanic oceanic archipelagos of the Azores, Madeira, Salvages, Canary Islands, and Cape Verdes located in the North Atlantic Ocean. The flora of the region demonstrate many characteristics typical of oceanic archipelago floras, notably a high degree of endemism, several spectacular examples of evolutionary radiations, and a distinctive growth form spectrum in the endemic flora with a much higher proportion of woody and succulent taxa than in the near-continent flora (e.g., Shmida and Werger 1992). Argyranthemum (Compositae), the subject of Chris Humphries’s doctoral research (see Humphries 1973, 1975, 1976a, 1976b) provides an excellent example of island evolution in region. Endemic to Macaronesia , Argyranthemum comprises twenty-four species of woody perennials. Molecular data support the monophyly and radiation of the genus in the region (Francisco-Ortega et al. 1997) and indicate that its closest relatives are herbaceous and distributed in North Africa. These findings are consistent with a scenario in which both woodiness evolved in response to insularity and the group radiated in Macaronesia following colonization from the near-continent. Other examples of groups showing similar Beyond Cladistics: The Branching of a Paradigm, edited by David M. Williams and Sandra Knapp.Copyright byThe Regents of the University of California.All rights of reproduction in any form reserved. 102 / BOTANY characteristics include the Aeonium alliance (seventy-five species; Mort et al. 2002), Echium (29 species; Böhle et al. 1996) and Sonchus (twentynine species; Lee et al. 2005). In 1979, Chris Humphries published a paper entitled “Endemism and Evolution in Macaronesia” that reviewed patterns of floristic diversity in the Macaronesian region and discussed the evolution of the region’s endemic flora. The paper also introduced cladistic concepts into the study of the endemic flora for the first time. While no explicit cladistic analyses were presented, the paper highlighted the need for cladistic principles to guide investigations of Macaronesian diversity. Since the publication of Humphries (1979), cladistic methodology has been widely applied to the study of Macaronesian endemic groups. Carine et al. (2004) reviewed sixty-four molecular cladistic analyses of Macaronesian endemic plant lineages that collectively accounted for approximately 32 percent of the endemic flora. The intervening 5 years have seen a further FIGURE 7.1 Location of the Macaronesian archipelagos of the Azores, Madeira, Salvages, Canary Islands, and Cape Verdes. Cabo Espichel in Portugal is also indicated as the flora of this headland includes endemic species of Euphorbia and Convolvulus considered to have evolved through back-colonization from the Macaronesian islands. The maximum age of each archipelago is given in parentheses. Cabo Espichel Azores (8.12) Madeira (15) Salvages (24–27) Canary Islands (20.5) Cape Verdes (10.3) 500km E NDEMI SM OF MACARONESI AN F LORA / 103 substantial increase in the number of published cladistic analyses such that the relationships of more than ninety Macaronesian endemic lineages have now been analyzed within a cladistic framework. These collectively represent over 50 percent of the endemic flora (Table 7.1). While variable both in terms of sampling of taxa and characters and in terms of the degree to which relationships are resolved, they nevertheless provide a rich resource for the study of Macaronesian diversity. In this chapter, we consider the impact of cladistic analyses on our understanding of the Macaronesian flora, focusing specifically on three aspects. First, we consider the biogeographic relationships of Macaronesian plant groups, building on the analyses of Carine et al. (2004) and Andrus et al. (2004) and incorporating more recent results. Second, we consider the impact of cladistic analyses, together with other analyses of regional diversity patterns, on our understanding of patterns of intraregional radiations. Finally, we consider the distinctive growth form spectrum of Macaronesian endemic plants (Shmida and Werger 1992) and present a preliminary evaluation of the extent to which woodiness in Macaronesia may be associated with insularity and linked to intraregional diversification. THE RELATIONSHIPS OF MACARONESIAN ENDEMIC PLANT GROUPS Table 7.1 presents data on the relationships of seventy-three genera and alliances with endemic taxa represented in the Macaronesian islands derived from published molecular phylogenetic analyses. Groups such as Euphorbia, Limonium, and Lotus, have not been included because published studies of these groups are extremely limited in sampling of either...