Divergence estimates of Tetrachondra hamiltonii and T-patagonica (Tetrachondraceae) and their implications for austral biogeography

The enigmatic genus Tetrachondra has been included variously in the Boragin aceae, Lamiaceae, Scrophulariaceae, or recognised as the distinct family Te trachondraceae. Two species with a disjunct distribution are included in th e genus: T. hamiltonii is confined to New Zealand, and T. patagonica is con fined to South America. New Zealand and South America once formed part of G ondwana, but separated approximately 80 million years ago. In a parsimony a nalysis of rbcL sequences, T. hamiltonii and T. patagonica form a distinct, well-supported clade that diverged early in the evolutionary history of th e large angiosperm order Lamiales. Polypremum procumbens emerges as their s ister group. While there are no known fossils of Tetrachondraceae, fossils from related families in the Lamiales suggest that the Tetrachondral/Polypr emum lineage may have evolved during the Paleocene. The rbcL sequences of T . hamiltonii and T. patagonica are virtually identical, however, suggesting a more recent divergence during the Pleistocene for these two species. Thu s, their present disjunct distribution reflects long-distance dispersal rat her than vicariance.