Abstract
The buckwheat family Polygonaceae is a diverse group of plants and is a good model for investigating biogeography, breeding systems, coevolution with symbionts such as ants and fungi, functional trait evolution, hybridization, invasiveness, morphological plasticity, pollen morphology and wood anatomy. The main goal of this study was to obtain age estimates for Polygonaceae by calibrating a Bayesian phylogenetic analysis, using a relaxed molecular clock with fossil data. Based on the age estimates, we also develop hypotheses about the historical biogeography of the Southern Hemisphere group Muehlenbeckia. We are interested in addressing whether vicariance or dispersal could account for the diversification of Muehlenbeckia, which has a “Gondwanan” distribution.Eighty-one species of Polygonaceae were analysed with MrBayes to infer species relationships. One nuclear (nrITS) and three chloroplast markers (the trnL-trnF spacer region, matK and ndhF genes) were used. The molecular data were also analysed with Beast to estimate divergence times. Seven calibration points including fossil pollen and a leaf fossil of Muehlenbeckia were used to infer node ages.Results of the Beast analyses indicate an age of 110.9 (exponential/lognormal priors)/118.7 (uniform priors) million years (Myr) with an uncertainty interval of (90.7–125.0) Myr for the stem age of Polygonaceae. This age is older than previously thought (Maastrichtian, approximately 65.5–70.6 Myr). The estimated divergence time for Muehlenbeckia is 41.0/41.6 (39.6–47.8) Myr and its crown clade is 20.5/22.3 (14.2–33.5) Myr old. Because the breakup of Gondwana occurred from 95–30 Myr ago, diversification of Muehlenbeckia is best explained by oceanic long-distance and maybe stepping-stone dispersal rather than vicariance. This study is the first to give age estimates for clades of Polygonaceae and functions as a jumping-off point for future studies on the historical biogeography of the family.
Highlights
The buckwheat family Polygonaceae Juss. with approximately 1,200 species [1] is morphologically diverse and growth forms include trees, shrubs, vines, lianas and herbs
Maximum Likelihood and MRBAYES analyses resulted in the same phylogenetic relationships (Fig. 1, tree files in Appendix S4)
Phylogenetic Relationships Results of the current MRBAYES and Maximum Likelihood (ML) analysis (Fig. 1) of one nr (ITS) and three cp markers for the most part show the same results for the evolutionary relationships among and within all genera included when compared to the ML and Maximum Parsimony analyses of other studies (e.g., [1], [22], [23], [51], [52])
Summary
The buckwheat family Polygonaceae Juss. with approximately 1,200 species [1] is morphologically diverse and growth forms include trees, shrubs, vines, lianas and herbs. Polygonaceae are found in a wide range of habitats from the Arctic to the tropics, from montane to lowland regions, and from arid to aquatic situations. Few synapomorphies exist for the entire group, but ocreae are found in most species. Even though Polygonaceae are not considered a group of great economic value, some species are used as crops and in horticulture. Buckwheat (Fagopyrum esculentum Moench) is a staple in Russia and soba noodles made from its flour are popular in Japanese cuisine. Several species, such as Antigonon leptopus Hook & Arn., Persicaria perfoliata (L.) H.Gross and Reynoutria japonica Houtt. Several species, such as Antigonon leptopus Hook & Arn., Persicaria perfoliata (L.) H.Gross and Reynoutria japonica Houtt. are used as ornamentals and have become invasive outside their native range
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