Nothofagus biogeography revisited with special emphasis on the enigmatic distribution of subgenus Brassospora in New Caledonia

Dispersals versus vicariance events and the presence of subgenus Brassospor a in New Caledonia are two riddles of Nothofagus biogeography, a genus also distributed in New Guinea, New Zealand, South America, Southeast Australia , and Tasmania, Within a cladistic framework using the software COMPONENT 2 .0, we demonstrate that most parsimonious area cladograms (areagrams) sensu cladistic biogeography need not always be the most plausible explanation n or reflect alternative geological hypotheses, The most parsimonious Nothofa gus history sensu historical biogeography is reconstructed where a minimum of dispersed taxa is hypothesized and vicariance events are identified. A f ully resolved well-established Nothofagus phylogeny was reconciled with thr ee geological hypotheses (geograms) of East Gondwana break-up: (a) the conv entional view (b) an Australian-New Caledonian relationship, and (c) a biot ic interchange between New Guinea and New Caledonia. Fossils determined to subgenus were optimized to the predicted lineages in the reconciled tree. D ue to extensive extinctions, a maximum of three vicariance events are infer red, all being basal in the subgenera, an indication of subgeneric diversif ication prior to the break-up of Gondwana. Two taxa, N. gunnii and N. menzi esii, are hypothesized as being long-distance dispersed, The most parsimoni ous solution suggests a close relationship between New Guinea and New Caled onia, supporting a Brassospora colonization route, but this hypothesis fail s to predict numerous extinct lineages observed in the fossil record and th us must be rejected. The traditional break-up sequence of Gondwana is not t he most parsimonious solution, indicating one incongruent node, but causes no overall incongruence with the fossil record, Considering all parameters, the occurrence of Brassospora in New Caledonia is most parsimoniously expl ained as a single colonization event from New Zealand where the subgenus su bsequently went extinct in the Pliocene, (C) 2001 The Willi Hennig Society.