Premium
CECROPSIS LUCULENTUM GEN. ET SP. NOV.: EVIDENCE FOR HETEROSPOROUS PROGYMNOSPERMS IN THE UPPER PENNSYLVANIAN OF NORTH AMERICA
Author(s) -
Stubblefield Sara P.,
Rothwell Gar W.
Publication year - 1989
Publication title -
american journal of botany
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.218
H-Index - 151
eISSN - 1537-2197
pISSN - 0002-9122
DOI - 10.1002/j.1537-2197.1989.tb15122.x
Subject(s) - pennsylvanian , sporangium , biology , stele , botany , pteridophyte , leafy , tracheid , strobilus , taxodium , gymnosperm , megaspore , paleontology , fern , xylem , pollen , structural basin , spore , ovule
An anatomically preserved specimen of a woody, heterosporous pteridophyte has been discovered in Upper Pennsylvanian peat‐forming swamp deposits of eastern Ohio. The fossil is described as Cecropsis luculentum gen. et sp. nov. It consists of a protostelic shoot tip with helically‐arranged vegetative leaves, sporophylls and adaxial eusporangia. The stele is marginally mesarch, with five cauline protoxylem strands that produce leaf‐trace protoxylem in a helix that approaches 2/5. Dense wood surrounds the protostele. Secondary tracheids have reticulate bordered pitting on all walls. Rays are uniseriate and 1–2 cells high. Vegetative leaves are 2–3 cm long and are pinnately‐dichotomously branched into terete lobes. Sporophylls are somewhat more extensively webbed, with clusters of sporangia located above vascularized receptacles. Sporangia are sessile and globose, with a terminal dehiscence slit. Megasporangia and microsporangia appear to be intermixed. Most are empty, but a small number contain either fragments of bean‐shaped microspores with asymmetrical trilete sutures, or a single radial and trilete megaspore. The presence of gymnospermous protoxylem architecture and wood in this heterosporous pteridophyte place it within the circumscription of the Progymnospermopsida. However, features of the stele, leaves, sporangia, and extreme heterospory indicate that it does not conform to a presently recognized order. The Pennsylvanian occurrence and unique features of Cecropsis leave open to question whether it is phylogenetically, or only phenetically related to other members of the Progymnospermopsida.