Paliurus(Paliureae, Rhamnaceae) from the Miocene of East China and its Macrofossil-based Phylogenetic and Phytogeographical History

Abstract

The extant genus Paliurus Miller is divided into P. ramosissimus and P. spina‐christi groups and is diagnostically characterized by distinctive orbicular‐winged fruits with a trilocular (or often bilocular) ovary and basally triveined leaves with a subentire to serrate margin. Here, structurally preserved winged fruits and associated compressed leaves of Paliurus (Paliureae, Rhamnaceae) are reported from the Middle‐Upper Miocene Shengxian Formation of Tiantai, Zhejiang, eastern China. The fruits can be identified as Paliurus microcarpa Xiang‐Chuan Li sp. nov., the diagnostic characters of external morphology and anatomy of which differ from those of both extant and fossil generic members; the leaves can be designated as Paliurus sp. The species based on winged fruits, P. microcarpa, might represent an ancient intermediate link exclusively known across the P. ramosissimus and P. spina‐christi groups, showing a closer affinity to the P. ramosissimus group based on the resemblant smaller fruits with a narrower wing, and to the P. spina‐christi group based on the similar wing structure and texture, respectively. Morphological analyses of the present and previous fossil fruit records around the world indicate that diversification of Paliurus had begun in northern transpacific regions by the Late Eocene. The macrofossil records, i.e., fruits and leaves of Paliurus globally when projected on paleoenvironmental maps in view of changing continental positions through time (from Eocene to Miocene) display that the past distribution of the genus was much wider than the present and belongs to a tropical and warm temperate realm of the Northern Hemisphere. Therefore, the modern restricted disjunction in tropical and warm temperate regions of East Asia and South Europe (even eastwards West Asia) might represent glacial refugia for some of the generic ancient lineages to survive severe cold at least since the terminal Pliocene.

The influence of the Gondwanan breakup on the biogeographic history of the ziziphoids (Rhamnaceae)

“…from India, and † Archeopaliurus from South America (Chen et al., ; Correa et al., ; Singh, Prasad, Kumar, Rana, & Singh, ). Younger fossils of the ziziphoids are, however, also distributed in the Northern Hemisphere, such as multiple Eocene (and younger) taxa of Ziziphus and Paliurus (Burge & Manchester, ; Li et al., ), and the Late Miocene fossils of Ceanothus and Distigouania (Axelrod, , ; Chambers & Poinar, ). This supports a subsequent dispersal of ziziphoids from South to North.…”

Earliest fossil fruit record of the genus Paliurus (Rhamnaceae) in Eastern Asia

“…Actually, the dimensions of this Paliurus microcarpa species fall within the range of the variation known for P. favonii, and Li et al (2014) identified their fossil fruits as a new species because they disagreed with the concept described by Burge and Manchester (2008). They were of the opinion that fruit dimension should not be used to differentiate species (for details see Li et al, 2014). For the modern species, all distinctive features, like leaf shape and fruit texture can, and should, be taken into consideration.…”

“…Schirarend & Olabi. (Figure 2p), has a thin and equatorially extended wide wing, with limited development of spongy parenchyma in the mesocarp (Burge and Manchester, 2008;Li et al, 2014). Even though there are some similarities between them and the Maoming samples, differences also exist.…”

“…Recently a Miocene species from Zhejiang Province, Paliurus microcarpa (according to the International Code of Nomenclature, the name should be Paliurus microcarpus) Li was recognized based on their small fruits and wing structure (Li et al, 2014). Actually, the dimensions of this Paliurus microcarpa species fall within the range of the variation known for P. favonii, and Li et al (2014) identified their fossil fruits as a new species because they disagreed with the concept described by Burge and Manchester (2008). They were of the opinion that fruit dimension should not be used to differentiate species (for details see Li et al, 2014).…”

“…However, there is a dramatic range contraction following the end of the Miocene. The genus went extinct from North America near the terminal Pliocene, resulting in the distribution of Paliurus being limited to Asia and Europe in the Pleistocene, which corresponds to the Maoming fossils 8.0-9.6 Narrow/Wide 3.0-5.0 na na na a) wing size <4 mm, narrow; wing size ≥4 mm, wide; na=not applicable; data from Chen and Schirarend (2007), Burge and Manchester (2008), Li et al (2014). range of extant species (Burge and Manchester, 2008). On the basis of these fossil records, Paliurus is considered to have originated in North America, with subsequent spread to Asia, and then to Europe (Manchester, 1999;Burge and Manchester, 2008).…”