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Reproductive and Vegetative Structure of Nordenskioldia (Trochodendraceae), a Vesselless Dicotyledon from the Early Tertiary of the Northren Hemisphere

Peter R. Crane, Steven R. Manchester and David L. Dilcher
American Journal of Botany
Vol. 78, No. 10 (Oct., 1991), pp. 1311-1334
Stable URL: http://www.jstor.org/stable/2445271
Page Count: 24
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Reproductive and Vegetative Structure of Nordenskioldia (Trochodendraceae), a Vesselless Dicotyledon from the Early Tertiary of the Northren Hemisphere
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Abstract

Nordenskioldia borealis Heer is described and its systematic position is reassessed based on examination of the type material and specimens recently collected from three Paleocene localities in North America (Almont, North Dakota; Melville, Montana; Monarch, Wyoming). The morphology of Nordenskioldia infructescences and fruits is clarified, and in particular, silicified specimens from Almont provide new details of fruit and seed anatomy. Fruits are schizocarpic, and individual fruitlets also dehisce to release flat reticulate seeds. These seeds occur in many Paleocene floras but have not been linked previously to Nordenskioldia. Anatomical details of infructescence axes are identical to those of distinctive long and short shoot systems that cooccur with Nordenskioldia, and neither the infructescence axes nor shoots have vessels in the secondary xylem. Comparison of the floras at Almont, Melville, and Monarch with those at other Paleogene localities in Asia, Europe, and North America provides association evidence supporting earlier conclusions that the Nordenskioldia plant bore simple, entire- to crenate-margined leaves with actinodromous venation. Such leaves have been previously assigned to extant genera such as Cercidiphyllum, Cocculus, and Populus but are treated here as Zizyphoides flabella (Newberry) comb. nov. Based on the combined morphological and anatomical details now available, the Nordenskioldia plant is assigned to the Trochodendrales as an extinct genus most closely related to extant Trochodendron.

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