Palaeobiogeographic studies of gymnospermous and dicotyledonous plants are numerous. But studies on the distribution history of monocotyledonous taxa are quite rare.

Prof. ZHOU Zhekun and his team of Xishuangbanna Tropical Botanical Garden (XTBG) of the Chinese Academy of Sciences elucidated the expansion of Cladium (Cyperaceae), a swampy herb genus encompassing about four extant species, during the late Cenozoic. 

The researchers collected about 100 fossil fruits from Sanzhangtian, Zhenyuan, Yunnan, China (24°06′N, 101°13′E; 1000 m a.s.l.), located in the southern foot the 3100 m high of Ailao Shan.  

The fossil fruits are oblong or obovate with three distinct and longitudinal sulcate sutures with the base of the endocarps spread outwards in to three protrusions. Cells of the epicarp are rectangular with straight wall, mexocarps are thin and cell walls of endocarp are undulate. 

The researchers compared the fossil fruits with extant and other fossil species of Cladium. Fossil materials from Zhenyuan are distinguished from other fossil species in shape, size, and base.  

Consequently, they ascribed the fossil fruits from the Middle Miocene of Zhenyuan, China, to a new species and named it as Cladium zhenyuanensis X. Q. Liang & Z. K. Zhou sp. nov.. 

The discovery of more than 100 fruit fossils of Cladium zhenyuanensi at the southern foothills of Ailaoshan implied that a mire landscape existed in the region in the middle Miocene and C. zhenyuanensis was probably a dominant component of the aquatic plant. 

 According to fossil data, Cladium first occurred in West Siberia in the Late Eocene. It evolved into a new species adapting to a different climate and environment in Southwest China. 

Cladium zhenyuanensis is the first fruit fossil record of Cladium from China. 

The study entitled “New fossil record of Cladium (Cyperaceae) from the Middle Miocene of Zhenyuan, SW China, and the palaeobiogeographical history of the genus” has been published in Review of Palaeobotany and Palynology. 

Fruits of Cladium zhenyuanensis sp. nov. from the Middle Miocene of Zhenyuan, China. (Image by LIANG Xiaoqing)