FORANIA PLEGIOSPINOSA, GEN. ET SP. NOV.: A ZOSTEROPHYLL FROM THE EARLY DEVONIAN OF NEW BRUNSWICK, CANADA, WITH A NOVEL EMERGENCE TYPE

摘要

Premise of research. The zosterophylls are a group of primitive land plants that possess comparatively few characters useful in taxonomic distinction but vary considerably among these characters, such that a large number of genera and species are currently recognized. We studied specimens of a novel Early Devonian plant from New Brunswick, Canada, that further extends known variation within Zosterophyllopsida sensu Kenrick and Crane. After careful reevaluation of character and character-state utility in taxonomic circumscription among these simple early plants, we recognize this plant as a new genus and species, Forania plegiospinosa. Methodology. Preserved as adpressions, specimens were prepared with the standard paleobotanical techniques of degagement and maceration, with appropriate parts figured via LM. Pivotal results. Forania plegiospinosa is interpreted to be a decumbent plant, bearing stout, mostly retrorsely curved, spine-like emergences arranged in two rows along the axes, variable modes of branching, circinately coiled axes, lateral buds, and sparsely scattered, circular to reniform lateral sporangia. Cuticular features of this species include polygonal epidermal cells and anomocytic sporangia. This plant provides the first documented evidence of stomata on emergences. The presence of stomata on the bases of large emergences suggests that emergence volume is a factor in stomatal location and development. Conclusions. Criteria for establishing new genera are discussed in the context of the mosaic of characters found among these early plants. Forania exhibits a unique combination of characters that is consistent with other zosterophylls at the generic level. It best fits within the Sawdoniaceae sensu Kenrick and Crane, although its sporangia are solitary rather than in two rows.