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First published online September 17, 2009; doi:10.3732/ajb.0800422 American Journal of Botany 96: 1849-1860 (2009) © 2009 Botanical Society of America, Inc.

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Spore wall ultrastructure in the early lycopsid Leclercqia (Protolepidodendrales) from the Lower Devonian of North America: Evidence for a fundamental division in the lycopsids¹

² Department of Animal and Plant Sciences, University of Sheffield, Alfred Denny Building, Western Bank, Sheffield S10 2TN, UK ³ Department of Biology, CB# 3280, Coker Hall, The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-3280 USA ⁴ Department of Biology, University of Wisconsin-Eau Claire, Eau Claire, Wisconsin 54701 USA

ABSTRACT

Documenting the morphology and ultrastructure of spores from known Silurian-Devonian plants clarifies organization and probable affinities of dispersed spores and contributes to analyses of evolutionary changes and phylogenetic relationships in early plants. In this study of fossil in situ spores from the early protolepidodendralean lycopsid Leclercqia, we identified new characters including an additional synapomorphy of the ligulate lycopsid clade. A detailed light (LM), scanning electron (SEM), and transmission electron microscope (TEM) analysis of spores from two species of Leclercqia from the Lower Devonian (Emsian) of New Brunswick, eastern Canada, L. andrewsii and L. complexa, shows both are homosporous, yielding spores belonging to the dispersed spore form taxon Acinosporites lindlarensis. Important features of wall ultrastructure include the presence of a paraexospore, peculiar exospore-derived, peg-like structures located in the gap between the outer exospore/inner paraexospore, and multilamellate regions in the interradial areas of the proximal surface. Similar interradial multilamellate regions occur in other ligulate lycopsids (fossil and extant). This character is probably a further synapomorphy for the ligulate lycopsid clade, within which heterosporous lycopods form a monophyletic group. These data suggest the ligule and interradial multilamellate region appeared prior to heterospory.

Key Words: Devonian • early land plants • fossil • Leclercqia • lycopsids • Protolepidodendrales • spores • ultrastructure

Received for publication 16 December 2008. Accepted for publication 18 May 2009.

FOOTNOTES

¹ This research was funded by NERC grant NE/E006612/1 to CHW.

⁵ Author for correspondence (e-mail: taylorwa{at}uwec.edu)

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