Stem Anatomy Confirms Tingia unita Is a Progymnosperm

SIMPLE SUMMARY: The systematic position of Noeggerathiales was long uncertain until the whole plant species Paratingia wuhaia was restored and proved to belong to progymnosperms due to its spore-producing fertile organ and secondary wood producing a large stem. However, whether Tingia Halle as the most diversified genus in Noeggerathiales belongs to progymnosperms has yet remained uncertain as the anatomy of the main stem of this plant is unknown, that is, whether the anatomy of the main stem with the anatomical characteristics of gymnosperms woods remains uncertain. Here, the stem anatomy of Tingia unita is presented based on fossil materials from the early Permian Wuda Tuff Flora in Wuda Coalfield, Wuhai City, Inner Mongolia, China. The well-developed secondary wood, plus previously accumulated evidence of the spore-bearing nature of this plant, confirms that this genus belongs to progymnosperms. As such, the genera Tingia and Paratingia are all certainly progymnosperms in affinity. ABSTRACT: Tingia Halle, a representative genus of the Cathaysia Flora, has been studied for nearly 100 years, being a small heterosporous tree based on the gross morphology of Tingia unita. However, the systematic affinity of Tingia is uncertain. Now, a number of well-preserved fossils of T. unita from the Taiyuan Formation of Lower Permian in Wuda Coalfield, Wuhai City, Inner Mongolia facilitates an examination of wood anatomy. The stem anatomy of T. unita shows parenchymatous pith, endarch primary xylem, pycnoxylic secondary xylem, and cortex, typically a type of gymnosperm wood, which taken together with pteridophytic reproduction, certainly evidences that Tingia Halle is a progymnosperm. In addition, Tingia together with Paratingia provide strong evidence to link the Noeggerathiales with progymnosperms.