The floristic differentiation of Southwest China: Insights from Cedrelospermum and Ailanthus fossils

doi:10.17520/biods.2022348

Abstract

Abstract:

Aims: Northwest Yunnan-Xizang and Southeast Yunnan-West Guangxi are two regions with distinct differences in pedigree age and appearance in southwestern China. The two regions are characterized by young flora dominated by herbaceous plants and ancient flora dominated by woody plants, respectively. It is unknown how the floristic differentiation of these two regions has formed.

Methods: We report new fossil records of Cedrelospermum and Ailanthus from the two study regions. We also review the fossil history of the two genera, particularly those in Southwest China.

Results: The fossil history of the two genera in Southwest China is as follows: Cedrelospermum occurred in the middle Eocene to late Oligocene of Xizang (C. tibetica) and the late Eocene of Southeast Yunnan (C. asiaticum). Ailanthus appeared in the middle Eocene to late Oligocene of Xizang (A. maximus) and the late Eocene of Southeast Yunnan (A. confucii). Our results show that both Northwest Yunnan-Xizang and Southeast Yunnan-West Guangxi floras grew Cedrelospermum and Ailanthus in the Paleogene, but the species are different since the late Eocene.

Conclusion: The genus level similarity of Northwest Yunnan-Xizang and Southeast Yunnan-West Guangxi floras support the hypothesis that floristic exchanges have occurred between the two regions. However, the difference in species indicates that the two floras have separated from each other since or before the late Eocene due to environmental differentiation. The woody Cedrelospermum and Ailanthus have disappeared from Xizang, and have been replaced by a generally younger herbaceous flora. In contrast, Ailanthus occurs presently in Southeast Yunnan, providing evidence for the archaic nature of the flora. Our study provides fossil evidence for the similarity and differentiation of the floras of Northwest Yunnan-Xizang and Southeast Yunnan-West Guangxi in the geological past.

Key words: Southwest China, Paleogene, floristic evolution, Ulmaceae, Simaroubacea

Linbo Jia, Tao Su, Weicheng Li, Shufeng Li, Yongjiang Huang, Zhekun Zhou. The floristic differentiation of Southwest China: Insights from Cedrelospermum and Ailanthus fossils[J]. Biodiv Sci, 2022, 30(11): 22348.

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URL: https://www.biodiversity-science.net/EN/10.17520/biods.2022348

https://www.biodiversity-science.net/EN/Y2022/V30/I11/22348

Figures/Tables 8

Fig. 1 The fossil localities in Xizang and Yunnan that yielded fossils of Cedrelospermum and Ailanthus, respectively

Fig. 2 Fossil fruits of Cedrelospermum tibeticum from Shenzha, Xizang. fb, Fruit body; v, Veins on the wing; w, Primary wing; g, Gap between the wings.

Fig. 3 Fossil fruit of Ailanthus confucii from Maguan, Southeast Yunnan. ss, Stylar scar; m, Margin of the winged fruit; vv, Ventral vein.

Fig. 4 The line drawings of Cedrelospermum fruit fossils from Southeast Yunnan and Xizang. A, C. tibeticum from the late Oligocene of Shuanghu, Xizang; B, C. tibeticum from the late Eocene of Shenzha, Xizang; C, C. asiaticum from the late Eocene of Maguan, Yunnan.

Fig. 5 The line drawings of Ailanthus fruit fossils from Southeast Yunnan and Xizang. A, A. maximus from the late Oligocene of Shuanghu, Xizang; B, A. confucii from the late Eocene of Maguan, Yunnan.

Fig. 6 The hypothesized floristic differentiation of Southwest China. A, Cedrelospermum tibeticum from the late Oligocene of Shuanghu, Xizang; B, C. tibeticum from the late Eocene of Shenzha, Xizang; C, Ailanthus maximus from the late Oligocene of Shuanghu, Xizang; D, Koelreuteria kvacekii from the middle Eocene of Bange, Xizang; E, Sabalites tibetensis from the late Oligocene of Shuanghu, Xizang; F, C. asiaticum from the late Eocene of Maguan, Yunnan; G, H, A. confucii from the late Eocene of Maguan, Yunnan; I, K. sp. from the late Eocene of Maguan, Yunnan; J, Craigia sp. from the late Eocene of Maguan, Yunnan; K, Sabalites sp. from the late Eocene of Maguan, Yunnan; L, Meconopsis pseudointegrifolia; M, Incarvillea younghusbandii; N, Rheum alexandrae; O, P, A. altissima; Q, K. bipinnata; R, Craigia yunnanensis; S, Livistona jenkinsiana. Scale bar = 5 mm.

Fig. 7 The changes of position and paleoenvironment of Cedrelospermum and Ailanthus fossil localitiesin Southwest China since the Eocene. The purple triangles show the location of the fossil localities, and the numbers correspond to the fossil localities in Table 1.

Table 1 Fossil occurrences of Cedrelospermum and Ailanthus in Southwest China. CD, Cedrelospermum; AL, Ailanthus.

编号 No.	化石点 Fossil site	时代 Age	类群 Taxon	经度 Longitude	纬度 Latitude	参考文献 Reference
1	西藏班戈 Bange, Xizang	中始新世 Middle Eocene	椿榆属 CD 臭椿属 AL	90.03	31.63	2019 2020
2	西藏尼玛 Nima, Xizang	晚始新世 Late Eocene	椿榆属 CD 臭椿属 AL	87.76	31.8	2019 2019
3	西藏申扎 Shenzha, Xizang	晚始新世 Late Eocene	臭椿属 AL	89.15	32.33	本研究 This study 2019
4	西藏双湖 Shuanghu, Xizang	晚渐新世 Late Oligocene	椿榆属 CD	89.76	32.03	2019
5	青海海西 Haixi, Qinghai	渐新世 Oligocene	臭椿属 AL	~91.2	~38.07	2020
6	云南马关 Maguan, Yunnan	晚始新世 Late Eocene	椿榆属 CD 臭椿属 AL	104.38	23.01	本研究 This study 2015
7	云南文山 Wenshan, Yunnan	早渐新世 Early Oligocene	臭椿属 AL	104.28	23.33	2013
8	广西宁明 Ningming, Guangxi	晚渐新世 Late Oligocene	臭椿属 AL	107.1	22.12	2014

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