Resolving the relationships of the enigmatic Sapotaceae genera Beauvisagea and Boerlagella, and the position of Planchonella suboppositifolia

The pantropical plant family Sapotaceae currently includes 65–70 genera. Two genera, Beauvisagea and Boerlagella, were described in 1890s using incomplete material from West New Guinea (Bird's Head Peninsula) and Sumatra, neither of which has been collected since. Their systematic position has long been regarded doubtful and Boerlagella was once placed in its own family, Boerlagellaceae. We show here how useful and important it can be to obtain small leaf fragments from type specimens that are up to 150 years old for molecular analysis aiming to determine their phylogenetic position and clarify their taxonomic status. We used nuclear ribosomal DNA (ETS, ITS) and the nuclear gene RPB2 from 170 terminals to estimate phylogenetic relationships in a Bayesian framework using BEAST. The old type material yielded full length sequences of ETS and ITS from both genera (less successful with RPB2), revealing that both are firmly placed in Planchonella. Boerlagella is placed in synonymy with Planchonella and its type is accepted as Planchonella spectabilis, a species from Sumatra that possibly has gone extinct due to deforestation. Beauvisagea from the Bird's Head Peninsula of western New Guinea is likewise regarded as a synonym of Planchonella and its type, accepted as P. pomifera, is conspecific with Pouteria doonsaf (currently circumscribed to include material of at least two different species), not Planchonella maclayana as earlier believed. Our study also included Planchonella suboppositifolia, an odd species with a character combination in conflict with the current definition of the genus. Our results show that it is sister to a lineage comprising several genera, including Planchonella, and that it represents a distinct lineage constituting a monotypic genus that will be described in a subsequent paper. The most recent classification of subfamily Chrysophylloideae and the character combinations used to distinguish its constituent genera are supported, and our results confirm that taxa can reliably be assigned to a genus based on morphology alone.