Resolving basal lamiid phylogeny and the circumscription of Icacinaceae with a plastome-scale data set

PREMISE OF THE STUDY: Major relationships within Lamiidae, an asterid clade with similar to 40 000 species, have largely eluded resolution despite two decades of intensive study. The phylogenetic positions of Icacinaceae and other early-diverging lamiid clades (Garryales, Metteniusaceae, and Oncothecaceae) have been particularly problematic, hindering classifi cation and impeding our understanding of early lamiid (and euasterid) character evolution. METHODS: To resolve basal lamiid phylogeny, we sequenced 50 plastid genomes using the Illumina sequencing platform and combined these with available asterid plastome sequence data for more comprehensive phylogenetic analyses. KEY RESULTS: Our analyses resolved basal lamiid relationships with strong support, including the circumscription and phylogenetic position of the enigmatic Icacinaceae. This greatly improved basal lamiid phylogeny off ers insight into character evolution and facilitates an updated classifi cation for this clade, which we present here, including phylogenetic defi nitions for 10 new or converted clade names. We also off er recommendations for applying this classifi cation to the Angiosperm Phylogeny Group (APG) system, including the recognition of a reduced Icacinaceae, an expanded Metteniusaceae, and two orders new to APG: Icacinales (Icacinaceae + Oncothecaceae) and Metteniusales (Metteniusaceae). CONCLUSIONS: The lamiids possibly radiated from an ancestry of tropical trees with inconspicuous fl owers and large, drupaceous fruits, given that these morphological characters are distributed across a grade of lineages (Icacinaceae, Oncothecaceae, Metteniusaceae) subtending the core lamiid clade (Boraginales, Gentianales, Lamiales, Solanales, Vahlia). Furthermore, the presence of similar morphological features among members of Aquifoliales suggests these characters might be ancestral for the Gentianidae (euasterids) as a whole.