Ryberg, Patricia E. , Taylor, Edith L. , Taylor, Thomas N. .
Buds and Branching in the Triassic sphenophyte Spaciinodum collinsonii.
Spaciinodum collinsonii is an herbaceous sphenophyte from the Middle Triassic Fremouw Formation of Antarctica. Stem fragments, most especially buds, have been found throughout the Triassic deposit. Buds are approximately 1.25 cm in length and 8.6 mm in diameter. Internodal length at the base of the buds is approximately 0.63 mm and 0.22 mm near the apex. Vascularization of the bud is not apparent in longitudinal section and rhizome attachment is not observed. Each node produces a whorl of six leaves. Leaves extend from nodes at 90° and then curve upward to enclose up to six nodes above. The base of each leaf is broad, but begins to taper as the leaves curve upward. Foliar vascular bundles contain small tracheids (11-22 μm in diameter) and thin-walled, presumed phloem cells (6-13 μm in diameter). One bud contains a whorl of six branches at the seventh node, each enclosed in the primary leaf sheath or ochreole. None of the branches have ruptured the top of the sheath indicating that they are immature. This represents the first evidence of branching in Spaciinodum. The ochreoles appear oval in cross section and measure 2.7 x 2.3 mm in diameter. The sheaths are simple, consisting of a single layer of wedge-shaped cells measuring 0.34–0.77 mm. No ornamentation is present on the surface and no vascularization is present in the ochreoles. Each branch primordium contains a ring of vascular bundles; bundles alternate with ridges on the surface of the branches. By analogy to modern Equisetum, the presence of buds in Spaciinodum suggests that aerial branches died back to the rhizome during the dark period of the Antarctic winter. The buds then provided new aerial growth the following spring.
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1 - University of Kansas, Department of Ecology & Evolutionary Biology, Natural History Museum and Biodiversity Research Center, 1200 Sunnyside Avenue, Lawrence, Kansas, 66045-7534, USA
Presentation Type: Oral Paper:Papers for Sections
Location: Williford A/Hilton
Date: Monday, July 9th, 2007
Time: 8:45 AM