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Abstract Detail

Paleobotanical Section

Smith, MaKenzie [1], ROTHWELL , GAR W [2], STOCKEY , RUTH A [1].

Evolution of the Osmundaceae: Osmundacaulis in the Northern Hemisphere.

A new species of Osmundacaulis (Osmundaceae) has been identified in a marine concretion from the Cumshewa Inlet, Queen Charlotte Islands, B.C., Canada.  The specimen comes from the Lower Cretaceous Haida Formation of the Queen Charlotte Group.  The preserved trunk segment is 27 cm long, up to 8 cm in diameter, consisting of a stem 16-18 mm in diameter surrounded by stipe bases, and interspersed diarch adventitious roots.  As is characteristic of Osmundacaulis species, this fern has a radial upright trunk, a dictyostele from which leaf traces diverge helically, and an inner cortex roughly as wide as the sclerenchymatous outer cortex.  The stele has 15 – 17 meristeles that are 20 – 35 tracheids thick.  Stipes are densely packed, diverge from the stem at 20 – 30 degrees, and extend up to 10 cm before truncating at the abraded periphery.  The pith shows incompletely preserved thin-walled cells with nests of sclereids and an outer sclerenchymatous sheath of thick-walled fibers, and lacks medullary bundles.  Each frond trace diverges from two adjacent meristeles as a C-shaped bundle, one to two tracheids thick, with two or three protoxylem strands.  One side of the trace separates from the stelar meristeles at a slightly lower level than the other.   As a leaf trace forms, sclerenchyma originates between the meristeles from which the trace will diverge.  Progressing distally, the sclerenchyma is at first solid and then becomes U-shaped, with a lobed peripheral margin that diverges from the stele on the adaxial side of the leaf trace xylem.  Stipes have a single C-shaped xylem bundle with protoxylem strands that increase to as many as 21 distally. Leaf traces are amphiphloic, immersed in thin-walled tissue, with interspersed sclerotic nests.  Stipes have a homogeneous sclerotic sheath, and an outermost homogenous zone of thinner-walled cells expanded laterally into short stipular wings. The height/width ratio of the stipe bases is ca. 1:1.3 in cross section.  This fossil has a novel combination of characters that reveals the presence of a third Northern Hemisphere species of the predominantly Southern Hemisphere genus Osmundacaulis.  The three Northern Hermisphere species of this genus, from Late Jurassic and Early Cretaceous, come from North America, with two coming from Lower Cretaceous deposits of the Queen Charlotte Islands.  Small fragments of gymnosperm wood, a protostelic gleichenaceous fern rhizome, a cupressaceous conifer leafy shoot, and a dispersed cunninghamioid needle are preserved within the stipe bases of the Osmundacaulis trunk. 

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1 - Oregon State University, Department of Botany and Plant Pathology, 2082 Cordley Hall, Corvallis, OR, 97331, USA
2 - Ohio University, Department of Environmental and Plant Biology, Athens, OH, 45701, USA

Lower Cretaceous.

Presentation Type: Oral Paper:Papers for Sections
Session: 21
Location: Whitewater/Grove
Date: Tuesday, July 29th, 2014
Time: 9:00 AM
Number: 21003
Abstract ID:475
Candidate for Awards:None

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