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Abstract Detail



Paleobotanical Section

Dunn, Michael [1].

Leaf trace production of selected Devonian and Mississippian seed ferns.

The analysis of a large data set of more than 70 permineralized stems, plus roots and numerous frond segments suggests that Tetrastichia bupatides, Laceya hibernica, and Tristichia spp. are closely related taxa. Characters such as phyllotaxy, rachis forking patterns, secondary xylem production and rachis trace morphology exhibit too much phenotypic plasticity to separate these taxa. At least at the generic level. However, this clade of stems can be identified by a consistent mode of rachis trace production. Cauline protoxylem strands are located approximately midway between the center of the stele and the apex of each arm, and rachis trace formation is initiated by the division of a protoxylem strand, producing two radially oriented strands. The distal strand then divides producing two tangentially oriented strands. The distal protoxylem strands divide a number of times and the trace then diverges from the stele. This mode of leaf trace production persists from at least the late Famennian where Laceya was described to the late Tournaisian where Tetrastichia was described and that this character is so highly conserved suggests that it might serve as a reliable character to segregate hydrasperman seed ferns into smaller clades. This project analyses the mode of rachis trace production of the earliest seed ferns such as Elkinsia, and the lyginopterid and calymopityacean seed ferns and compares those characters to the tetrastichians in attempt to interpret persistent patterns that may unite these taxa.

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1 - CAMERON UNIVERSITY, 2800 Gore Blvd, LAWTON, OK, 73505, USA

Keywords:
Devonian
Hydrasperman seed ferns
Mississippian
rachis trace production.

Presentation Type: Oral Paper:Papers for Sections
Session: 12
Location: Melrose/Riverside Hilton
Date: Monday, July 29th, 2013
Time: 2:30 PM
Number: 12005
Abstract ID:261
Candidate for Awards:None


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