Age Estimates for the Buckwheat Family Polygonaceae Based on Sequence Data Calibrated by Fossils and with a Focus on the Amphi-Pacific Muehlenbeckia

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.

Tertiary montane origin of the Central Asian flora, evidence inferred from cpDNA sequences of Atraphaxis (Polygonaceae)

“…We believe that this discrepancy results in part from the different sequences used, but is probably mainly due to the present analysis adding more species samples within the genus, which in practice can change the tree topology and sequence variability. In any case, both we and Schuster et al () hypothesize an origin and diversification of Atraphaxis in the Older Tertiary Eocene‐Oligocene. This hypothesis of an Eocene‐Oligocene origin of Atraphaxis is similar to that for Artemisia (Asteraceae) (Miao et al ), a cosmopolitan grassland genus mainly inhabiting arid and semiarid regions, that originated in the late Eocene, with development mainly in the Miocene, in arid and semiarid Central Asia.…”

“…As mentioned, our dated times of stem age of approximately 47 Ma and crown age of approximately 27 Ma for Atraphaxis , are greater than the recent dating of 35.2–40.8 Ma and 19.6–22.6 Ma, respectively, by Schuster et al (). We believe that this discrepancy results in part from the different sequences used, but is probably mainly due to the present analysis adding more species samples within the genus, which in practice can change the tree topology and sequence variability.…”

“…We used the uncorrelated lognormal relaxed clock model with a Yule process for the speciation model, GTR + I + G for the substitution model (estimated for the dataset). Recently, a comprehensive dating of Polygonaceae (Schuster et al ) has been carried out, in terms of its outline and pollen fossil of Polygonaceae (Gray ; Muller ), and we utilized four constraints: (i) the root of Polygonaceae at approximately 70 Ma (prior normal, mean = 70 Ma, SD = 1); (ii) a pollen fossil of Calligonum 5.3–2.6 Ma (prior exponential); (iii) Calligoneae 63–35 Ma (stem‐crown of Schuster et al , prior I exponential offset 35, mean 63; prior II uniform, lower 35, upper 70); and (iv) Polygonum‐Atraphaxis 39–35 Ma (stem‐crown of Schuster et al , prior I exponential offset 35, mean 39; prior II uniform, lower 35, upper 70). A Markov chain Monte Carlo (MCMC) was run for 50 million generations and sampled every 1,000 generations, and two independent runs for priors I and II were performed to confirm convergence of the analysis.…”

Phytochemical and biological research of Polygoneae medicinal resources

“…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. Age estimates for Polygonaceae were obtained by calibrating a Bayesian phylogenetic analysis (Schuster et al, 2013), using a relaxed molecular clock with fossil data. Interspecific hybridization and the following polyploidization play a major role in plant diversification, but quantifying the contribution of this mechanism to diversification within taxonomically complex clades remains difficult.…”

Flora do Ceará, Brasil: Polygonaceae

“…No entanto, com base em análises de DNA, Polygonaceae foi considerada como pertencente à Caryophyllales, tendo como grupo-irmão Plumbaginaceae (APG III 2009;Souza & Lorenzi 2012). Em Polygonaceae são reconhecidas duas subfamílias caracterizadas principalmente pela presença (Polygonoideae) ou ausência (Eriogonoideae) de ócrea (Mabberley 2008;Schuster et al 2013). Destaca-se que Polygonoideae tem ampla distribuição na área de ocorrência da família (Mabberley 2008) e Eriogonoideae está restrita ao novo mundo (Kempton 2012).…”