Phylogeny and Historical Biogeography of Geraniaceae in Relation to Climate Changes

Chloroplast (trnL–F and rbcL) sequences were used to reconstruct the phylogeny of Geraniaceae and Hypseocharitaceae. According to these data Hypseocharitaceae and Geraniaceae are monophyletic. Pelargonium and Monsonia are sisters to the largest clade of Geraniaceae, formed by Geranium, Erodium and California. According to molecular dating and dispersal-vicariance analysis, the split of the stem branches of Geraniaceae probably occurred during the Oligocene, in southern Africa or in southern Africa plus the Mediterranean area. However, their diversification occurred during the Miocene, coinciding with the beginning of major aridification events in their distribution areas. An ancestor of the largest clade of Geraniaceae (Geranium, Erodium, and California) colonised a number of habitats in the northern hemisphere and in South American mountain ranges. In summary, the evolution of the Geraniaceae is marked by the dispersal of ancestors from Southern Africa to cold, temperate and often disturbed habitats in the rest of world, where only generalist pollination and facultative autogamy could ensure sufficient seed production and survival. Keywords—autocompatibility, dispersal-vicariance, drought-tolerance, molecular dating, nectaries, P/O indexes. The Geraniaceae are included in the order Geraniales along with the families Francoaceae, Greyiaceae, Ledocarpaceae, Melianthaceae and Vivianiaceae (Soltis et al. 2000; APG II 2003). A number of molecular and morphological studies have included the monogeneric family Hypseocharitaceae within the family Geraniaceae (Boesewinkel 1988; Rama Devi 1991; Price and Palmer 1993; APG II 2003) but they are separated by some morphological features such as fruit and carpel structure (Hutchinson 1969; Slanis and Grau 2001). Phylogenetic relationships were examined in four genera: Geranium (Price and Palmer 1993; Pax et al. 1997), Pelargonium (Bakker et al. 1998, 1999, 2000, 2004, 2005), Erodium (Fiz et al. 2006), and Monsonia (Touloumenidou et al. 2007). The phylogenetic study of Geraniaceae using rbcL sequences by Price and Palmer (1993) showed Sarcocaulon to be included in Monsonia (Albers 1996a, 1996b; Albers and Löbbert 1996), and Pelargonium to be sister to the other four genera of Geraniaceae. The inclusion of Sarcocaulon in Monsonia was also supported by data on ITS and trnL–F (Touloumenidou et al. 2007). According to Price and Palmer (1993), Erodium and Geranium are phylogenetically close, and California could be a sister group of the subclade formed by Erodium and Geranium (Aldasoro et al. 2002; Fiz et al. 2006). Geraniaceae have a worldwide distribution but are best represented in Southern Africa. Pelargonium has about 270 species centered in the Cape Floristic Region, Succulent Karoo, Nama Karoo, and KwaZulu-Natal while a lower number of species are found in east Africa, Australia, Madagascar, St. Helena, and Tristan da Cunha (Bakker et al. 1998, 1999, 2005). The 39 species of Monsonia inhabit Africa and southwestern Asia (Kers 1968; Moffett 1979; Venter 1979, 1983; Albers 1996a, b). Erodium has 74 species and shows its greatest diversity in the Mediterranean area (Guittonneau 1972; ElOqlah, 1989; Aldasoro et al. 2000), while California only inhabits western North America (Aldasoro et al. 2002). Geranium is the largest of the family, comprising about 420 species distributed all over the world (Fig. 1; Yeo 1973; Aedo et al. 1998, 2002). Price and Palmer (1993) proposed that Hypseocharis could be the sister taxon to Geraniaceae. Hypseocharis grows in subalpine habitats of the central Andes (Boesewinkel 1988, 1997; Slanis and Grau 2001). Many members of Geraniaceae are characteristic of the Afro-Arabian land mass (Hutchinson 1969). The differentiation of these genera can be associated with adaptation to desert and steppe environments, which became progressively more extended in Africa and Arabia during the end of the Tertiary (Kers 1968; Venter 1983). The other members of the family are characteristic of today’s northern temperate continents, and occupy more mesic environments (Yeo 1984, 1990; Boesewinkel