封印木在石炭纪–二叠纪欧美植物群的沼泽森林中占据重要地位, 化石记录十分丰富, 在华夏植物群中的记录则较为稀少。已知这类植物的孢子叶球都是单性的。本文基于内蒙古乌达煤田下二叠统太原组凝灰岩中的化石材料, 报道了一种石松类双性孢子叶球类型, 与封印木茎干及叶保存于原位埋藏的火山凝灰岩植物群中, 共同构成封印木树冠。该类孢子叶球呈圆柱形, 基部具柄; 孢子叶紧密螺旋排列, 近轴部分为水平伸出的孢子叶柄, 远轴部分为上翘的远端叶片, 两者转折处具明显的踵; 孢子囊单生于孢子叶柄近轴面, 大孢子囊位于孢子叶球的中部－基部, 小孢子囊位于中部－顶部。该类双性封印木孢子叶球的发现增加了封印木繁殖器官的多样性和复杂性, 为进一步探讨这类植物的系统分类与演化提供了重要信息。
Sigillaria Brongniart is a fossil genus of arborescent lycopsids and so far known only producing monosporangiate strobili, including Sigillariostrobus Schimper, Mazocarpon Benson and Nudasporestrobus Feng et al. As one of the dominant com-ponents in the Carboniferous–Permian Euramerican swamps, Sigillaria possesses abundant fossil records in Euramerica and comprehensive researches on its reproductive organs have been conducted. However, fossil records of sigillarians in Cathaysia, especially reproductive organs, are relatively rare. Based on well-preserved specimens from the Asselian Taiyuan Formation of Wuda Coalfield, Inner Mongolia, this pa-per presents a new type of bisporangiate strobilus, associated with stem and leaves of Sigillaria in the autochthonous Wuda Tuff Flora (Chinese “vegetational Pompeii”) and together forming a crown. The bisporangiate strobili are cylindrical with a slender peduncle. Sporophylls are arranged in helix, with a horizontal pedicel as the proximal part, an upward distal lamina as the distal part, and an abaxial heel in the transitional part between the proximal and distal parts of sporophyll. Sporangia are borne on adaxial surface of the pedicel. Megasporangia are located in the basal portion of the strobili and each one contains over 70 megaspores. Microsporangia are located in the apical portion. Trilete megaspores are ca. 500 μm in diameter, with oval amb, and the distal surface is laevigate; trilete circular microspores are 30–40 μm in diameter, with finely microgranulate sculpture. This is the first record of bisexual strobili with organic connection to Sigillaria. In the present case, the bisporangiate strobili are organically connected to Sigillaria cf. S. ichthyolepis (Presl) Corda, the upper-canopy tree of the peat-forming vegetation, i.e. the Wuda Tuff Flora. In consideration of the fundamental distinction between monosporangiate and bisporan-giate strobili, sigillarians might be a polyphyletic group. The new bisporangiate strobili appear to be primitive by a r–selection strategy to increase natality. In brief, the current bisporangiate strobili of Sigillaria indicate a higher diversity and more complexity on the reproduc-tive strategy of sigillarians than previously understood, and provide significant information on the systematics and evolution of the genus.