Sj. Wagstaff et al., Divergence estimates of Tetrachondra hamiltonii and T-patagonica (Tetrachondraceae) and their implications for austral biogeography, NZ J BOTANY, 38(4), 2000, pp. 587-596
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.