The Biogeographic South-North Divide of Polygonatum (Asparagaceae Tribe Polygonateae) within Eastern Asia and Its Recent Dispersals in the Northern Hemisphere

Abstract

Eastern Asia (EA) is a key region for the diversification of flowering plants in the Northern Hemisphere, but few studies have focused on the biogeographic history within EA in the context of the other northern continents. Polygonatum is an important medicinal genus widely distributed in the Northern Hemisphere with its highest species richness in EA, and it represents an excellent model for studying the evolution of biogeographic patterns in this region. Divergence time estimation was used to examine the biogeographic history of Polygonatum based on nuclear ITS and four plastid sequences (rbcL, matK, psbA–trnH and trnC–petN) from 30 Polygonatum species and 35 outgroup taxa. The ancestral area of Polygonatum and subsequent dispersal routes were inferred using Bayes-Lagrange. Polygonatum was estimated to have originated in southern EA during the middle Miocene (14.34–13.57 Ma) with subsequent south-to-north expansion in the late Miocene. Multiple intercontinental dispersal events were inferred between EA and Europe or North America, and all of them have occurred recently in the late Miocene to Pliocene. The separation of Polygonatum into the south and north lineages and their subsequent diversifications in the late Miocene supports the existence of a biogeographic divide between the northern and southern parts of EA that also coincides with the retreat and redevelopment of the arid zone in EA in the Neogene. Our results demonstrate the complexity of biogeographic history of Polygonatum in the Northern Hemisphere including early vicariance followed by frequent and recent dispersals in the Neogene.

Phylogenetic relationships and biogeographic history of the unique Saxifraga sect. Irregulares (Saxifragaceae) from eastern Asia

“…It has often been suggested that the east-west-orientated aridity belt acted as a climate barrier between nEA and sEA (Donoghue et al, 2001;Guo et al, 2008;Bai et al, 2016). A similar pattern was also reported for Polygonatum, Pistacia, and Quercus, that the arid zone acted as a barrier of their gene flow between southern and northern parts of EA (Xie et al, 2014;Wang et al, 2016;Deng et al, 2018). Our biogeographic results also revealed multiple recent migrations/exchanges between nEA and sEA in the late Miocene to present (Fig.…”

“…The Asian/North American disjunctions can be explained by the Bering land bridge, which was available until 3.5-5.0 Ma (Elias et al, 1996); this dispersal route played a significant role for the initial range expansion of Saxifraga to Asia and for further dispersal throughout the Northern Hemisphere (Ebersbach et al, 2017a). The Bering land bridge dispersal route has been proposed for a number of other plant groups (Nie et al, 2006(Nie et al, , 2007Zhu et al, 2013;Wei et al, 2015;Wang et al, 2016;Wen et al, 2016;Graham, 2018). Although the North Atlantic land bridges were also available in the Oligocene, they seem less likely because there are no records of extant species or fossils of sect.…”

“…The disjunct distribution of plants between EA and North America have fascinated many botanists and biogeographers (Boufford & Spongberg, 1983;Tiffney, 1985;Lee et al, 1996;Wen, 1999;Nie et al, 2006Nie et al, , 2007Nie et al, , 2010Meng et al, 2008;Wang et al, 2016;Xie et al, 2016). The EA/North American disjunctions have commonly been documented in Saxifraga and any other genera in Saxifragaceae (Zhu et al, 2013;Deng et al, 2015;Ebersbach et al, 2017a) and the sect.…”

“…East Asia is a pivotal region for the biogeographic diversification of flowering plants in the Northern Hemisphere with one of the highest levels of species diversity and endemism (Wu & Wu, 1998) and been suggested to be the ancestral area for many EA–eastern North American disjunct lineages (Wen, 1999; Donoghue et al, 2001; Milne & Abbott, 2002; Wen et al, 2010). Biogeographic studies of flowering plants in the Northern Hemisphere have largely focused on the classical EA and North American disjunctions, however, few studies were devoted to exploring biogeographic patterns within EA at the same time (but see studies from Zhu et al (2013), Wen et al (2014), and Wang et al (2016)). A better understanding of the biogeographic pattern within EA and its connections to the other continents could provide important insights into the biogeographic history of the Northern Hemisphere.…”

A new synonym of Polygonatum in China, based on morphological and molecular evidence

“…Tamura et Ogisu from Polygonatum (Tamura et al 1997a) and found the topological difference of Heteropolygonatum and its relative taxa: (1) (Heteropolygonatum + Disporopsis) + Polygonatum and (2) (Heteropolygonatum + Polygonatum) + Disporopsis (Tamura et al 1997b). Later, the former case was supported by Meng et al (2014) and Wang et al (2016), whereas the latter one was supported by Floden and Schilling (2018) and Zhao et al (2019). The genus Polygonatum was divided into three sections, based on four chloroplast molecular markers, leaf arrangement and basic chromosome number: (1) Polygonatum sect.…”