Evolution and biogeography of Pleurophyllum (Astereae, Asteraceae), a small genus of megaherbs endemic to the subantarctic islands.

Premise Of The Study: The abundance of fossils in Antarctica suggests this continent was a center of diversification and a corridor for migration for many austral plant groups until the late Tertiary and may have played a pivotal role in shaping plant distributions in the southern hemisphere. Although the Antarctic flora was largely erased by glaciation during the Pleistocene, at least some Antarctic plant species found refuge on the subantarctic islands.

Methods: We used independent and combined analyses of ITS, ETS, trnK, and trnL DNA sequences to infer phylogenetic relations in Pleurophyllum, a small genus of three species that are endemic to the subantarctic islands of Australia and New Zealand. The inferred phylogeny provided a framework to reconstruct the origin and patterns of diversification in the genus.

Key Results: We summarize support for the hypothesis that Pleurophyllum survived episodes of Pleistocene glaciation in the subantarctic islands and that its sisters dispersed northward in response to glacial advance.

Conclusions: The distinctive flora of the subantarctic islands includes some of the last remnants of a once-diverse Antarctic flora. These plants may still retain distinctive features of their ancestors. Studies of endemic plants such as Pleurophyllum are the key to resolving this puzzle.