Abstract Detail

Paleobotany

Gensel, Patricia G [1].

More “woody” plants from the Early Devonian.

Evidence is building that either there are several plants or several occurrences of a small number of plants with an early type of secondary xylem. The two currently described ones are Armoricaphyton chateaupannense from the Pragian of France (Gerrienne et al., 2011 and Strullu-Derrien et al, 2014) and Franhueberia gerriennii from the Emsian of south shore of Gaspé Bay, Quebec, Canada (Hoffman and Tomescu, 2013). These plants, as well as the ones surveyed below are comparatively narrow in width (less than 1 cm) and exhibit P-type secondary wall thickenings in their tracheids, suggesting they may represent basal euphyllophytes. Gerrienne et al. (2011) included information about a third, as yet undescribed taxon from the Emsian of New Brunswick, Canada for which some data are presented here. Fairly short lengths of 3-5 mm wide ribbed axes exhibit both equal and unequal branches. Preserved xylem consists of an elongate-oval primary xylem strand with a central region of protoxylem. This stele exhibits lateral trace departure from either end. Some axes exhibit both primary and secondary xylem. The secondary xylem consists of regular rows of up to 24 tracheids, interspersed by spaces interpreted as rays, and evidence of multiplicative divisions. Permineralized isolated nodules from the same locality but showing no morphology also yield axes with poorly preserved primary xylem and extensive secondary xylem. The axes divide isotomously. Comparison with previously known taxa is difficult but tentatively, these axes are somewhat similar to Franhueberia. Alternatively, they may be more similar to roots (unusual in the Early Devonian), represent more mature regions of the plant above or a very different taxon. To better determine affinity, more details of the primary xylem are needed Lastly, some slender axes from the Emsian of the north shore of Gaspé, strongly resembling Psilophyton, exhibit a haplostele with centrarch primary xylem and possible secondary growth, being rather similar to Armoricaphyton. Long sequences, including regions of branching, are being studied. Clearly much more needs to be learned about variability in stelar organization and presence/absence of secondary xylem in plants which, on the basis of characters currently available, appear to represent part of the basal euphyllophytes. Their significance relative to evolution of progymnosperms and/or early seed plants is presently unclear, but they may indicate an early establishment of lignophyte characters.

1 - University Of North Carolina, Department Of Biology, 414 Coker Hall, University Of North Carolina, CHAPEL HILL, NC, 27599-3280, USA

Keywords:
secondary wood
euphyllophyte
Devonian.

Presentation Type: Oral Paper
Session: 23, Paleozoic and Mesozoic Paleobotany
Location: 102/Savannah International Trade and Convention Center
Date: Tuesday, August 2nd, 2016
Time: 8:45 AM
Number: 23003
Abstract ID:786
Candidate for Awards:None