Ancient divergence and biogeography of Raukaua (Araliaceae) and close relatives in the southern hemisphere

Abstract

Molecular genetic analyses were used to reconstruct phylogenetic relationships and estimate divergence times for Raukaua species and their close relatives. A monophyletic group identified as the ‘greater Raukaua clade’ was circumscribed, with eight representative species; its basal divergence was estimated at c. 70 Mya, possibly after Zealandia had separated from Gondwana. Raukaua is paraphyletic because of the placement of Motherwellia, Cephalaralia, Cheirodendron and Schefflera s.s. The phylogeny supports a more narrowly circumscribed Raukaua that includes the New Zealand but not the South American or Tasmanian representatives. Ancestors of the monophyletic South American and Tasmanian Raukaua and the mainland Australian Motherwellia and Cephalaralia diverged at c. 66 Mya and their current disjunction may be vicariant, with overland dispersal between Australia and South America, possibly via Antarctica. Vicariance is also a likely mechanism for divergence at c. 57 Mya of the monophyletic Motherwellia, Cephalaralia and Tasmanian Raukaua. The common ancestor of New Zealand Raukaua¸ Cheirodendron and Schefflera s.s. is inferred to have existed c. 62 Mya in New Zealand, before the marine incursions during the Oligocene, implying that New Zealand Raukaua and Schefflera s.s. survived the inundation period or speciated outside New Zealand and subsequently colonised. Ancestors of Cheirodendron split from New Zealand Raukaua c. 43 Mya and dispersed over vast expanses of the south-western Pacific to Hawaii.