A well preserved big Cycadeoidea (Cycadeoidaceae, Bennettitales) fossil trunk has recently been found from the Cretaceous strata in Darhan Muminggan Joint Banner, Baotou City, Inner Mongolia. The trunk in columnar shape measures 56cm in height and 48cm in maximum diameter. It consists of central pith, peripheral xylem cylinder, petiole bases and cones from the central part to the outside. The dense rhombic bases of the petiole are helically arranged on the surface of the trunk. The petiole bases decrease in size from the base to the apex of the trunk, with cones unevenly scattered in between. This specimen is the first complete fossil trunk of Cycadeoidea found in China. The fossil wood of Xenoxylon latiporosum (Cramer) Gothan (Gymnosperm) is recognized near the fossil trunk. The trunk and other fossil woods are important materials for studying the evolution of Cycadeoidea and the composition of Cretaceous flora in northern China.%内蒙古包头达尔罕茂明安联合旗发现了保存完整的白垩纪大型本内苏铁目拟苏铁科拟苏铁属（Cycadeoidea）茎干化石。茎干化石呈椭球形，保存完好，高56cm，最大直径48cm，化石表面密布的菱形叶柄基呈螺旋状排列，从基部至顶端叶柄基逐渐变小，球果不均匀散生于叶柄基之间。茎干化石从内到外包括中央的髓部、外围的木质部圆筒、叶柄基、球果等。这是国内首次发现保存比较完整的本内苏铁目拟苏铁科茎干化石。同时，在茎干化石产地附近还发现有裸子植物宽孔异木(Xenoxylon latiporosum (Cramer) Gothan)木化石。本内苏铁茎干及宽孔异木化石对于研究本内苏铁目的演化历史和当时的植物群组成特点具有重要的科学意义。
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