Abstract Detail

Paleobotany

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

An anatomically preserved Early Devonian rhyniopsid from the Battery Point Formation (Gaspé, Canada).

The Battery Point Formation (Gaspé Peninsula, Québec) hosts a rich Early Devonian (Emsian) flora including plant compressions and permineralizations. The latter represent one of the rare occurrences of anatomically-preserved Early Devonian plants and rival in diversity the classic Rhynie chert permineralized flora. Among the anatomically-preserved plants of the Battery Point Formation, a type of tracheophyte that had not been identified previously is represented by >10 axes. Axes of this plant are up to 2.1 mm in diameter and 2.5 cm long. The central xylem strand is 0.5-1.9 mm in diameter, surrounded by a thin layer of tissue with thin-walled cells, interpreted as phloem. This layer, ca. 50 µm across, is 3-cells thick, with elongated cells. Outside the phloem, the cortex consists of thicker-walled cells often exhibiting dark content (which is also seen in some phloem cells). Cortical cells are elongated and 25-50 µm in diameter. The thickness and topography of the cortex vary widely. Some of the thicker axes have a thin cortical layer, ca. 120 µm and 3-4 cells thick, with an outer surface forming squat deltoid protrusions (410 µm wide at base and 190 µm tall). Other thick axes, as well as the thinnest specimen exhibit a cortical layer with prominent protrusions that can exceed 1 mm in height and have irregular shape and arrangement. The most striking feature of this Gaspé plant is the color of its xylem, which is a lighter brown hue compared to that of other plants in the assemblage, suggesting different cell wall chemistry. The xylem has centrarch maturation, with round to oval tracheids reaching 70 µm in diameter close to the periphery (although size decreases slightly in the outermost tracheids). Tracheids exhibit very robust S-type wall thickenings forming a helical pattern with gyres 20 µm or more apart. Thickenings are 12 µm wide at the base and protrude into the tracheid lumen ca. 7 µm. S-type tracheids characterize a group of rhyniopsids – Rhynia, Stockmansella, Huvenia, Taeniocrada dubia, Sennicaulis, and Sciadophyton. The Gaspé plant is very similar in its terete centrarch xylem strand and the overall tracheid wall thickening pattern to all these taxa, but differs from each of them in specific details of the structure and size of anatomical features. Furthermore, all these rhyniopsids have much higher axis:xylem diameter ratios (4:1 to 15:1) than the Gaspé plant (axis:xylem diameter 1:1 – 2.5:1), which probably represents a new type of rhyniopsid.

1 - Humboldt State University, Biological Sciences, 1 Harpst Street, Arcata, CA, 95521, USA

Keywords:
fossil
Devonian
Rhyniopsida
tracheid
xylem
permineralized
anatomy
Canada.

Presentation Type: Oral Paper
Session: 5, Paleobotany Student Awards
Location: 204/Savannah International Trade and Convention Center
Date: Monday, August 1st, 2016
Time: 8:15 AM
Number: 5001
Abstract ID:313
Candidate for Awards:Isabel Cookson Award,Maynard F. Moseley Award