Biogeography of Camphorosmeae (Chenopodiaceae): tracking the Tertiary history of Australian aridification

Camphorosmeae (Chenopodiaceae, formerly Sclerolaeneae) are widespread across all states of Australia. Molecular data revealed that the Australian Camphorosmeae represent a monophyletic lineage comprising 147 currently recognised species, 145 of which are endemic to Australia. Like their Eurasian relatives most Australian Camphorosmeae are well-adapted to dry and saline environments, and most species are distributed in semi-arid or arid landscapes of the Eremaean area of central and western Australia. The historical biogeography of the Australian Camphorosmeae is analysed using an ETS phylogeny of the group and DIVA. We found that diversification of the tribe started at the end of the Miocene, and that radiation took place during the Pliocene, probably driven by the aridification of Australia during this time. Southern west Australia probably served as the ancestral area, and we hypothesise that the ancestors of Australian Camphorosmeae were already adapted to dry and saline conditions and might have been distributed in coastal or saline inland habitats. Successful dispersal and establishment of Camphorosmeae in the then newly developed arid regions was probably enhanced by niche pre-emption. Our timing of the radiation of this drought-adapted lineage and the directions of its dispersal support the hypothesis that the aridification of Australia started during the Late Miocene and arid areas expanded during the Pliocene from the west to the east and then north. Telopea 13(1-2): 2011 Cabrera, Jacobs and Kadereit Australia, Camphorosmeae are distributed in southwestern Europe and northwestern Africa through the Mediterranean area and north Africa to eastern Asia. A few species also occur in South Africa and North America. Camphorosmeae is the most diverse tribe of Chenopodiaceae in Australia. The genera Sclerolaena (64 spp.) and Maireana (57 spp.), together with Atriplex (57 native, 56 of which are endemic, and 4 introduced spp.; Chenopodioideae), contain nearly 60% of the native species of Chenopodiaceae found in Australia (Wilson 1984). The degree of endemism of Camphorosmeae is 99% compared to 80% for Australian species in general (Crisp et al. 1999). Taxa of the tribe, although mainly adapted to arid and semi-arid conditions of the Eremaean area of central and western Australia, are present in all major areas of endemism sensu Crisp et al. (1999). Several species are salt or gypsum tolerant and their occurrence is linked to inland salt lakes. Some species extend into agricultural lands and coastal habitats where they tolerate slightly saline soils. Furthermore, species distribution varies significantly. For example, Roycea spinescens is restricted to saline sand and sandy clay areas from Morawa south to Merredin, Western Australia, while the widespread species Enchylaena tomentosa occurs throughout Australia and extends beyond the continent to New Caledonia. Recent molecular studies clearly support the monophyly of Camphorosmeae (Akhani et al. 2007, Kadereit et al. 2003, Kadereit & Freitag 2011) as well as the monophyly of the Australian genera (Cabrera et al. 2009, Kadereit et al. 2005). The origin of the Australian Camphorosmeae has been dated to the Late Miocene (8.1-3.6 mya, Kadereit et al. 2005) and to the Middle Miocene (16.4-10.3 mya; Kadereit & Freitag 2010), with a small clade of three annual species, Kochia melanoptera, K. krylovii and Bassia dasyphylla, distributed in Central Asia, being sister to the Australian lineage. These three Asian species are similar to the Australian species in performing C 3 -photosynthesis and showing a C 3 -sclerolaenoid leaf structure, in contrast to the majority of Eurasian species which are C 4 -plants (Cabrera et al. 2009). A new genus, viz. Grubovia Freitag & G.Kadereit was recently erected to accommodate these three species (Kadereit & Freitag 2011).