A marattialean trunk of Psaronius laowujiensis sp. nov. is described from the Upper Permian of the Xuanwei Formation, Panxian County, Guizhou Province, South China. The specimen most likely represents the lower part of the trunk, because the preserved thickness of the root mantel is somewhat larger than the diameter of the stem. Meristeles of the stem are arranged in approximately five tangential stelar cycles but not in radial files. Inner meristeles are in small number, similar to 12-13, and loosely arranged. Leaf traces diverge helically and are organized in a 2/5 phyllotaxy. The leaf base vascular configuration consists of three strands that include a large U-shaped, centrifugal strand, a small centripetal strand, and an inverted V-shaped internal strand. A vascular bundle sheath one or two cell layers thick surrounds each meristele. Within the centripetal concavity of each peripheral cauline bundle there are anchor-shaped sclerenchymatous strands. Ground tissue appears to consist of aerenchymatous parenchyma, in which secretory cavities are dispersed. Bound roots mostly possess seven to nine protoxylem poles. The vascular bundle sheath is one or two cell layers thick. The inner cortex consists of aerenchymatous parenchyma. A detailed comparison of the present specimen with known species of Psaronius from the Permian of South China is made. Our specimen is similar to Psaronius wangii in many aspects, but the two can be clearly distinguished by the structure of the ground tissue of the stem and the leaf base vascular configuration, which leads to the erection of a new species, P. laowujiensis, for this specimen. Certain important characters in species from the Permian of South China are discussed. The tree-or anchor-shaped sclerenchymatous configuration within the centripetal concavity of the peripheral cauline bundles is unique to species from the South China Permian. The permanent vascular bundle sheath surrounding the meristeles of the stem and the stele of the root is another remarkable feature of those species. The analogous tissue, termed "inner cortex" by certain authors, is also present in some Psaronius from the Euramerican and North China floras, but in those cases it is thinner walled and not as remarkable as the vascular bundle sheath in the species from South China. The leaf base vascular configuration of the species from the Permian in South China is more diverse than those from other places.