Abstract Detail



Paleobotany

Rothwell, Gar [1].

Cauline vascular architecture and leaf trace production of Early Permian Medullosa lucartii Goeppert and Stenzel.

Medullosan pteridosperms are among of the most structurally complex and frequently encountered of all Carboniferous and Permian gymnosperms.  Species are distinguished by a novel stem stele that typically consists of two or more segments of primary xylem, each of which is surrounded by secondary vascular tissues, and by fronds that are vascularized by several bundles that arise from the stem at two or more levels. Traditionally, that stellar structure was widely regarded as representing the coalescence of two or more stems that arose by the telomic process syngenesis.  However, in a stellar analysis of Pennsylvanian age Medullosa species from North America, Basinger et al. demonstrated that those stems have the equivalent of a eustele.  The current study employs the same methodology to investigate the more complex steles of the Early Permian Medullosa species that occur in the pyroclastic blow-down forest at Chemnitz, Germany.  In M. lucartii the stele consists of an outer zone of tangentially elongated vascular segments (=”snake rings” of early workers) and small interior “star rings”.  Protoxylem strands are located within the peripheral strands and are positioned near the outer margin of the metaxylem (i.e., are mesarch).   In a complete stem where the number can be counted there are 13, which corresponds to one of the expected numbers of the Fibonacci series.  Leaf trace emission areas are identified by absence of secondary vascular tissues at levels where traces diverge.  Often, such areas also are expanded toward the periphery of the stem.  Some leaf traces originate as small primary bundles, while others diverge as larger metaxylem areas.  The latter are characterized by secondary tissues that diminish in thickness distally, and divide into two or more bundles before extending into a leaf base.  In all of these features, the leaf trace emission pattern for M. lucartii is comparable to the more ancient medullosan species, and such stems can be recognized as having a modified eustele.


1 - Ohio University, and Oregon State University, Environmental and Plant Biology, and Botany and Plant Pathology, 308 Porter Hall, Ohio University, Athens, OH, 45701, USA

Keywords:
eustele
Medullosaceae
Medullosa lucartii
Early Permian
seed fern.

Presentation Type: Oral Paper
Number: 0003
Abstract ID:164
Candidate for Awards:None


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