Ambilobea, a new genus from Madagascar, the position of Aucoumea, and comments on the tribal classification of the frankincense and myrrh family (Burseraceae)

Phylogenetic analyses of 46 species, representing all tribes and 14 out of 18 recognized genera of Burseraceae, are performed using nuclear ETS and plastid rps16 sequences. Boswellia madagascariensis, the only Malagasy species of this genus, is shown to belong to a clade comprising all sampled members of the current tribe Canarieae plus Triomma, whereas other species of Boswellia (including the type, B. serrata) form a clade that is strongly supported as sister to Garuga. A new genus, Ambilobea, is proposed for B. madagascariensis and the new combination A. madagascariensis is made. Ambilobea differs from Boswellia s. s. by being dioecious and by having valvate petals and, furthermore, is unique in the family by its winged tips to the petioles, by having pyrenes that remain attached to the detached valves of the fruit at dehiscence, and by its long-spinose pollen grains. Aucoumea, a monotypic central African rain forest genus, is strongly supported as sister to a clade with the arid-adapted Bursera and Commiphora. Boswellia s. s. and Garuga form a clade characterized by having hermaphroditic flowers. The relationships within Burseraceae emerging from this and previous phylogenetic studies are, on several points, in conflict with current tribal delimitation. The following suggestions for a new tribal classification of Burseraceae are made: 1) Beiselia, sister to the rest of the family, needs to be placed in a tribe of its own, Beiselieae, trib. nov., 2) Protieae should be restricted to Crepidospermum, Protium and Tetragastris, although generic rearrangements seem to be needed within this tribe, 3) Bursereae should be restricted to Aucoumea, Bursera and Commiphora, but generic rearrangements are needed in the Bursera–Commiphora complex, 4) the remaining genera, Ambilobea, Boswellia, Canarium, Dacryodes, Garuga, Haplolobus, Pseudodacryodes, Rosselia, Santiria, Scutinanthe, Trattinnickia and Triomma, are probably best placed in a broadly circumscribed Garugeae.