Divergence times, historical biogeography, and shifts in speciation rates of Myrtales

• Improved phylogenetic resolution of plant order Myrtales with stronger support for placement of Combretaceae.
• Divergence times, biogeography and speciation rates estimated across the order.
• Albian–late Aptian crown radiation (∼116 Mya) estimated for the Myrtales.
• Strong Gondwanan affinity for all major lineages.
• Three shifts in speciation rates across Myrtales detected with BAMM that each span K–Pg boundary.

We examine the eudicot order Myrtales, a clade with strong Gondwanan representation for most of its families. Although previous phylogenetic studies greatly improved our understanding of intergeneric and interspecific relationships within the order, our understanding of inter-familial relationships still remains unresolved; hence, we also lack a robust time-calibrated chronogram to address hypotheses (e.g., biogeography and diversification rates) that have implicit time assumptions. Six loci (rbcL, ndhF, matK, matR, 18S, and 26S) were amplified and sequenced for 102 taxa across Myrtales for phylogenetic reconstruction and ten fossil priors were utilized to produce a chronogram in BEAST. Combretaceae is identified as the sister clade to all remaining families with moderate support, and within the latter clade, two strongly supported groups are seen: (1) Onagraceae + Lythraceae, and (2) Melastomataceae + the Crypteroniaceae, Alzateaceae, Penaeaceae clade along with Myrtaceae + Vochysiaceae. Divergence time estimates suggest Myrtales diverged from Geraniales ∼124 Mya during the Aptian of the Early Cretaceous. The crown date for Myrtales is estimated at ∼116 Mya (Albian–Aptian). BioGeoBEARS showed significant improvement in the likelihood score when the “jump dispersal” parameter was added. South America and/or Africa are implicated as important ancestral areas in all deeper nodes. BAMM analyses indicate that the best configuration included three significant shifts in diversification rates within Myrtales: near the crown of Melastomataceae (∼67–64 Mya), along the stem of subfamily Myrtoideae (Myrtaceae; ∼75 Mya), and along the stem of tribe Combreteae (Combretaceae; ∼50–45 Mya). Issues with conducting diversification analyses more generally are examined in the context of scale, taxon sampling, and larger sets of phylogenetic trees.

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