BISPORANGIATE STROBILI FROM THE TUFF FLORA OF THE LOWER PERMIAN TAIYUAN FORMATION, WUDA COALFIELD, INNER MONGOLIA
Article
Figures
Metrics
Preview PDF
Reference
Related
Cited by
Materials
Abstract:
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.
