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Invited Special Paper |
2 Department of Biological Sciences, State University of New York, Oswego, New York 13126 USA
ABSTRACT
Although flowers, leaves, and stems of the angiosperms have understandably received more attention than roots, the growing root tips, or root apical meristems (RAMs), are organs that could provide insight into angiosperm evolution. We studied RAM organization across a broad spectrum of angiosperms (45 orders and 132 families of basal angiosperms, monocots, and eudicots) to characterize angiosperm RAMs and cortex development related to RAMs. Types of RAM organization in root tips of flowering plants include open RAMs without boundaries between some tissues in the growing tip and closed RAMs with distinct boundaries between apical regions. Epidermis origin is associated with the cortex in some basal angiosperms and monocots and with the lateral rootcap in eudicots and other basal angiosperms. In most angiosperm RAMs, initials for the central region of the rootcap, or columella, are distinct from the lateral rootcap and its initials. Slightly more angiosperm families have exclusively closed RAMs than exclusively open RAMs, but many families have representatives with both open and closed RAMs. Root tips with open RAMs are generally found in angiosperm families considered sister to other families; certain open RAMs may be ancestral in angiosperms.
Key Words: angiosperms basal angiosperms eudicots meristem organization monocots phylogeny root apical meristems
Received for publication 1 February 2007. Accepted for publication 5 November 2007.
FOOTNOTES
1 Since C.H. started this project in the early 1950s, many persons helped to obtain seeds and plants or provided other assistance, and many graduate students helped section materials for slides. Among those identified are B. L. Turner, H. S. Irwin, H. S. Blomquist, C. A. Albers, M. Arif Hayat, T. N. Taylor, the late J. M. Byrne, T. Webster, J. E. Armstrong, L. Libous, D. Francko, D. A. White, R. Scribaio, J. Morris, J. A. Doyle, J. Dubrovsky, P. F. Stevens, an anonymous reviewer, E. L. Schneider, P. Bernhardt, S. McGabe, C. Peterson, D. Enstone, A. Soukup, O. Votrubová, P. W. Barlow, L. C. Marsh, D. Kelly, J. Welsh, M. Seago, C.H.s Miami University colleagues, and many others, especially the late D. Heimsch and C.H.s children, Richard, Carolyn Martinich, and Alan. The authors also express their appreciation to the University of Texas and Miami University for funding C.H.s early work and to botanical gardens around the world that provided seeds to C.H.
3 1914–2003, Emeritus Professor of Botany, Miami University, Oxford, Ohio
4 Author for correspondence (e-mail: seago{at}oswego.edu)
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