Abstract
BackgroundThe Solanaceae is a plant family of great economic importance. Despite a wealth of phylogenetic work on individual clades and a deep knowledge of particular cultivated species such as tomato and potato, a robust evolutionary framework with a dated molecular phylogeny for the family is still lacking. Here we investigate molecular divergence times for Solanaceae using a densely-sampled species-level phylogeny. We also review the fossil record of the family to derive robust calibration points, and estimate a chronogram using an uncorrelated relaxed molecular clock.ResultsOur densely-sampled phylogeny shows strong support for all previously identified clades of Solanaceae and strongly supported relationships between the major clades, particularly within Solanum. The Tomato clade is shown to be sister to section Petota, and the Regmandra clade is the first branching member of the Potato clade. The minimum age estimates for major splits within the family provided here correspond well with results from previous studies, indicating splits between tomato & potato around 8 Million years ago (Ma) with a 95% highest posterior density (HPD) 7–10 Ma, Solanum & Capsicum c. 19 Ma (95% HPD 17–21), and Solanum & Nicotiana c. 24 Ma (95% HPD 23–26).ConclusionsOur large time-calibrated phylogeny provides a significant step towards completing a fully sampled species-level phylogeny for Solanaceae, and provides age estimates for the whole family. The chronogram now includes 40% of known species and all but two monotypic genera, and is one of the best sampled angiosperm family phylogenies both in terms of taxon sampling and resolution published thus far. The increased resolution in the chronogram combined with the large increase in species sampling will provide much needed data for the examination of many biological questions using Solanaceae as a model system.
Highlights
The Solanaceae is a plant family of great economic importance
Divergence times are of major interest for studies of evolutionary biology and historical biogeography, and to researchers who focus on understanding various types of trait evolution, such as the development of chemical and genetic pathways, climatic niche and geographic range sizes, and morphological, ecological and behavioural characters
Of the two wood fossils, Solanumxylum paranensis can be clearly assigned to Solanaceae based on a large number of anatomical characters such as para- and apotracheal axial parenchyma that is diffuse in aggregates, simple perforation plates, bordered and alternate intervessel pits, homocellular rays, fibres that are polygonal and quandrangular in section, and the presence of septate fibers (Table 1) [49]
Summary
The Solanaceae is a plant family of great economic importance. Despite a wealth of phylogenetic work on individual clades and a deep knowledge of particular cultivated species such as tomato and potato, a robust evolutionary framework with a dated molecular phylogeny for the family is still lacking. Separate studies have explored relationships at tribal [23,24,25,26] and generic levels [27,28,29,30,31,32,33], and many phylogenetic studies have focused on Solanum, a genus that comprises nearly half of the species within the family [34,35,36,37,38,39,40]; see [21] for references prior to 2006] Some of these studies have resulted in taxonomic changes, such as recircumscription of the previously distinct genera Lycopersicon, Cyphomandra, Normania, and Triguera as parts of a monophyletic Solanum [35,41,42]. Sometimes disruptive in the short term, have helped to both stabilise names and provide a better evolutionary context for future studies
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