A kind of silicified fossil wood with mixed pits on the radial tracheid wall is described. The fossil wood was collected from the top of Taiyuan Formation (early Early Permian) in Wuda Mining District, Nei Mongol. Compared with the Paleozoic fossil woods in the world, it is put into Araucarioxylon Kraus and named as A. laoshidanense sp. nov. Based on the character of possessing mixed pittings (alternate and opposite pittings) on the radial tracheid wall, the fossil wood is believed to be one of the unknown primitive conifers.Diagnosis of the new species: Only secondary xylem preserved and consisting of axial tracheids and rays. Growth ring boundary, resin duct and axial parenchyma absent. One to Four (commonly 2or3) seriates of bordered pits mostly alternate but sometimes opposite）on the radial tracheid wall. One to Four (commonly1, rarely2 to 4) Cupressoid pits in each cross-field. Rays usually uniseriate, sometimes partly-biseriate and 2 to 39 (mainly3-5) cells high.
内蒙古早二叠世早期南洋杉型木属一新种
王士俊 胡雨帆 崔金钟
（中国科学院植物研究所，北京100093）
摘要：报道了一种具混合型纹孔（互列式纹孔和对列式纹孔）的化石木。化石木产自内蒙古乌达矿 区老石旦矿附近太原组上部，地质时代为早二叠世早期。经比较，确认为南洋杉型木属(A raucarioxylon Kraus)一新种：老石旦南洋杉型木(Araucarioxylon laoshidanense sp. nov.)。根据混合型纹孔的存在及其他特征，认为新种可能代表了一种原始的松杉 类植物的木材化石。主要特征： 仅保存有次生木质部，无生长轮，仅由轴向管胞和木射线构成，未见轴向薄壁 组织和树脂道。管胞排列紧密，径向壁具缘纹孔1～4列，其中2～3列者较常见。纹孔的排 列以互列紧挤为主，也有少量对列-亚对列的纹孔。交叉场内多具1～2个柏木式纹孔。木射 线多为单列，少数为部分双列，高2～39个(多为3～5个)细胞。
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