The Bark And Leaf Anatomy Of Ningxiaites Specialis Feng From The Sunjiagou Formation In Shitanjing Coalfield,Ningxia Huizu Autonomous Region

Conifers play a very important role in the late Permian floras. However, previous studies of the late Permian conifers were mainly based on leaf inpressions, their bark and leaf anatomy remains poorly understood. In recent years, the anatomical study of conifer wood provided great taxonomic information and evolutionary significance for the late Palaeozoic plants. The permineralized plant stem Ningxiaites specialis Feng from the Sunjiagou Formation in the Shitanjing Coalfield, Ningxia Huizu Autonomous Region was restudied in this paper. This is the first detailed description of conifer bark and leaf anatomical structures from the upper Palaeozoic of Cathaysia.Ningxiaites specialis Feng has exceptionally well-preserved extraxylary tissues, including vascular cambium and bark. The vascular cambium bears one or two layers of parenchymatous fusiform cells. The bark is ca.1.8mm thick, and comprised by a secondary phloem and periderm. The secondary phloem is divided into the young secondary phloem and the old secondary phloem, which consists of rays, axial paren-chyma and sieve cells. The young secondary phloem consists of rows of tangentially banded sieve cells and ray cells are abundant. In transverse section, the sieve cells are subcircular to polygonal, and30μm in diameter, their walls are up to2um thick. In longitudinal section, the sieve cells show long tubular outlines. The sub-circular sieve areas are confined to the radial walls of sieve cells and arranged in a single linear se-ries. Axial parenchyma cells are rare and irregularly distributed in the young second-ary phloem. The rays continue from the secondary xylem into the secondary phloem. The ray cells in the secondary phloem are inflated and larger than those in the sec-ondary xylem. The numbers of axial parenchyma cells are increased and ray cells are decreased in the old secondary phloem. The periderm consists of cork cells that are frequently filled with dark contents and regularly arranged.The leaf of Ningxiaites specialis Feng consists of epidermis, mesophyll and vascular tissues. The linear leaves helically arranged on the permineralized shoot axis. In transverse section, leaves various from semicircular to rectangular; epidermal cells are tightly arranged in one layer. The epidermis is covered by a thick cuticle and cy-lindrical or strip papillae. The mesophyll cells are differentiated into palisade tissue and spongy tissue. Stomatal bands are longitudinal arranged on one side of the leaf. The stomata composed of a pair of bean-shaped guard cells and a ring of subsidiary cells. The vascular tissue possesses vascular bundle and transfusion cells, that sur-rounded by an endodermis. The endodermis consists of one layer of parenchyma cells. Each leaf has one vascular bundle. Numerous small pits are present on the transfusion cell walls. Resin canal is absent in the leaf.