Study On The Stem Of The Late Permian Xuanwei Formation In Panxian County, Guizhou Province

Lepidodendrales are the most important elements of lycopsids, and all of them have the arborescent habit. They appeared firstly in the end of the Middle Devonian and extinct at the end of Permian. Members of this group were the most conspicuous plants of the coal-swamp ecosystems and also are responsible for extensive quantities of plant material that resulted in formation of Carboniferous and Permian coal seams around the world. In this paper, by using cellulose acetate peel technique, an anatomically preserved lepidodendralean stem from the Xuanwei Formation of Huopu coal mine, Panxian, Guizhou in Southwest China, have been studied in detail. Through in-depth analysis of the characteristics of this stem and comparing with other members of Lepidodendrales, a new genus, Lobatodendron gen.nov. and and a new species, Lobatodendron guizhouense gen. et sp. nov., are established. In addition, the significance on the taxonomy and evolution of Lepidodendrales of several typical characteristics are in this paper.Lobatodendron guizhouense gen. et sp. nov is arborescent and the lobate primary xylem is the most significant character. Besides, it pessesses the mixed characteristics of Sigillariaceae and Diaphorodendraceae:The outer margin of the primary xylem is undulated, forming ridges and troughs, leaf traces appear to originate from the troughs; phelloderm consists of alternating dark bands of secretory cells and light bands of other cells. All of these features are shared with Sigillaria. While the mixed pith is the feature of Diaphorodendron. The mixed characteristics owned by Lobatodendron guizhouense gen. et sp. maybe the result of a long-term evolution from the earlier Sigillaria or Diaphorodendron. This is the first detailed study on the well-preserved stems of Lepidodendrales from the late Permian of the Southwest of China, which enriches our knowledge about the anatomy and taxonomical diversity of lepidodendralean plants of the late Permian and bears implications on the phylogeny and late evolution of lepidodendralean plants.