Abstract Detail



Paleobotany

Pfeiler, Kelly [1], Tomescu, Alexandru [2].

A new type of Early Devonian wood-producing euphyllophyte from Gaspé (Canada).

The Battery Point Formation of Gaspé (Canada) hosts a broad diversity of Early Devonian (Emsian) plants with excellent potential for adding to the knowledge of early tracheophyte anatomy. A recently identified permineralized plant from this rock unit consists of a decorticated axis fragment at least 19 mm long and 2 mm in diameter. The plant has four-lobed central primary xylem with mesarch maturation and shows evidence of secondary growth. Metaxylem tracheids, 17-33 µm in diameter, have Psilophyton-type thickenings (and simple bordered pits in smaller cells). Crushed cells form lines along the mid-plane of the xylem lobes. Based on their position we infer presenceof several protoxylem strands along these areas, consistent with radiatopsid architecture. The secondary xylem is thicker in the bays between primary xylem lobes (0.32 mm) than around the lobe tips (0.24 mm), with correspondingly higher (up to 13) and lower (7-9) numbers of cells per tracheid file. Multiplicative divisions occur infrequently in the periphery of the axis. Secondary xylem tracheids,up to 42 µm in diameter, also have P-type thickenings. Uniseriate rays are incompletely preserved. Among coeval actinostelic plants, Gensel’s 1984 euphyllophyte, with three-lobed xylem, is larger than the new plant, has larger metaxylem tracheids, and lacks secondary growth. Leptocentroxyla, also lacking secondary xylem, has four-lobed xylem but larger metaxylem tracheids than the new plant. The Gaspéplant is comparable in its lobed primary xylem, protoxylem architecture, and secondary growth to Middle Devonian plants, including early progymnosperms (e.g. the aneurophyte Tetraxylopteris) and protostelic seed plants (e.g. Tetrastichia). Compared to these, the Gaspé plant has metaxylem tracheids half as small. Its secondary xylem tracheids are similar in size to those of Tetrastichia; in Tetraxylopteris, secondary xylem tracheids cover a broad size range, with the smallest sizes comparable to those of the Gaspé plant. The most useful term of comparison – anatomy of lateral trace divergence cannot be assessed, as the Gaspé plant does not preserve laterals. Irrespective of this, the new plant differs from aneurophytes and early seed plants in having P-type tracheids, which preclude taxonomic placement in these groups. Despite this, the features it shares with the aneurophytes indicate that this plant could be an aneurophyte precursor. This new Gaspé euphyllophyte adds to a growing diversity of Early Devonian wood-producing plants and is another representative of a recently emerging group that, intriguingly, combines anatomical features characteristic of younger euphyllophytes with a plesiomorphic type of tracheid pitting.


1 - 628 9th Street, Arcata, CA, 95521, United States
2 - 154 Grange Road, Eureka, CA, 95503, United States

Keywords:
euphyllophyte
fossil
Devonian
secondary growth
wood
progymnosperm.

Presentation Type: Oral Paper
Number: 0004
Abstract ID:508
Candidate for Awards:Isabel Cookson Award,Maynard F. Moseley Award


Copyright © 2000-2019, Botanical Society of America. All rights reserved