华北早二叠世鳞木类大孢子囊-孢子叶复合体—无被果孢属(Achlamydocarpon Schumacker-Lambry)的研究

本论文系统回顾了无被果孢属的研究历史，讨论了无被果孢属的鉴定特征及种的划分依据，总结了无被果孢属已有种的特征及分布。在此基础上对山西太原西山煤田太原组7号煤层煤核及河北平泉杨树岭煤矿太原组火山凝灰岩中的无被果孢属进行了详细的解剖学研究，把它们与无被果孢属已有种进行了详细的对比后，共鉴定出二个新种和二个未定种。这二个新种的主要特征如下： 过渡无被果孢（新种）Achlamydocarpon intermedia sp. nov. 大孢子囊大约长6.0－10.0 mm，宽4.6 mm，高1.4mm，背腹扁状，具顶脊，两侧角明显, 近轴端开口。孢子囊壁复杂，分化为三层：最外层为单层柱状细胞层;中层1－2层细胞厚，细胞具深色内含物，壁薄;内层1－3层细胞厚，细胞壁强烈加厚。柱状层朝近轴端方向厚度加大。大孢子叶柄背脊不甚发育，具明显侧翼，侧翼的末端膨大并下垂使得柄的横切面略呈 “M”形。侧翼的宽度由近轴端向远轴端随孢子囊宽度的增加而增加，整体宽度大致保持为孢子囊的宽度的1/2左右。侧翼的近轴面具对称的厚壁组织区域。木质部束在近轴端为近等径状，向远轴端则变为略呈水平伸长状。通气组织发达，独立空腔结构贯穿孢子叶柄的整个长度。败育大孢子似乎具肿块结构。 本新种产于山西太原西山煤田太原组7号煤层煤核中。 2、平泉无被果孢（新种） Achlamydocarpon pingquanensis sp. nov 大孢子囊10.0－15.0 mm长，8.1 mm宽，3.0 mm 高。背腹扁，不具顶脊，两侧角明显，远轴端开口。壁复杂，分化为5层：最外层为薄壁细胞层，厚1-3层细胞;次外层为次生壁强烈增厚的细胞层，厚2-数层细胞;中层为具深色内含物的薄壁细胞层，厚2-数层细胞;次内层为与次外层相似的厚壁细胞层;内层为厚度达数个细胞的薄壁细胞层。孢子叶柄侧翼发育，宽度大于孢子囊宽度。背脊或龙骨很不显著。远轴面有时呈强烈的起伏不平状。大孢子囊底部与孢子囊柄连结部分由厚壁的细胞构成。不育组织垫结构较显著。功能大孢子扁缩，在近轴端发育较好，上表面具一突起结构。败育大孢子瘪缩，结构复杂，具明显肿块结构（？），瘤状肿块结构与败育孢子表面相连部分呈棒状。孢子叶柄近轴面不具有明显的厚壁组织区域;维管束由木质部束、维管束鞘及其所围成的空腔组成，但在远轴端仅剩下木质部束;通气组织发达，在维管束下方形成一独立空腔。 本新种分别产于山西太原西山煤田太原组7号煤层煤核和河北平泉杨树岭煤矿太原组火山凝灰岩中。 过渡无被果孢（新种）的特征介于欧美植物区的变异无被果孢类型和塔赫他间无被果孢类型之间。平泉无被果孢（新种）则与变异无被果孢类型较相近，但二者的大孢子囊壁的最外层完全不同：前者的是柱状细胞层，而后者的则由近等径的类似薄壁组织的细胞构成。二个未定种中，无被果孢（未定种 1）与过渡无被果孢（新种）很相似，区别在于前者的大孢子囊壁缺乏最外层的柱状细胞层以及孢子叶柄具明显的背脊或龙骨。无被果孢（未定种 2）则与塔赫他间无被果孢类型较接近。 根据华夏植物区和欧美植物区的化石材料和文献，探讨了保存不完整的大孢子囊-孢子叶复合体的远轴端和近轴端的判断方法：孢子囊较宽较高、孢子叶柄较为粗大、侧翼较发育、维管束较大、通气腔较发育的一端往往为远轴端，反之则为近轴端。 还讨论了无被果孢属一些构造的演化趋势： 1、孢子囊壁由简单向复杂或高度分化; 2、通气组织由不发达到高度特异化; 3、叶迹从微弱到显著，从简单到复杂; 4、败育大孢子从饱满到瘪缩，从表面平整到高度曲折，结构复杂化 5、大孢子四分体结合紧密度呈下降趋势

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