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First published online September 17, 2009; doi:10.3732/ajb.0800385 American Journal of Botany 96: 1787-1797 (2009) © 2009 Botanical Society of America, Inc.

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Wollemia nobilis (Araucariaceae): Branching, vasculature and histology in juvenile stages¹

² Harvard Forest, Harvard University, 324 North Main Street, Petersham, Massachusetts 01366 USA ³ The Kampong of the National Tropical Botanical Garden, 4013 Douglas Road, Miami, Florida 33133 USA ⁴ Department of Chemistry, University of British Columbia Okanagan, 3333 University Way, Kelowna, British Columbia, V1V 1V7, Canada

ABSTRACT

We present a preliminary description of the morphology and anatomy of contrasted axes in the recently discovered conifer Wollemia nobilis, based on clonally propagated material. The novelty of this discovery and the tree’s size and rarity has led to global interest and a comprehensive and successful conservation program. Our results should serve as a model on which future studies of this tree and other members of the Araucariaceae can be based. The specimens studied are mimics of the architecture of the mature tree, with precise distinction between orthotropic (= trunk) axes, which have radial symmetry (spiral phyllotaxy) and plagiotropic (= branch) axes with dorsiventral symmetry (as a modified decussate phyllotaxy). Trunk axes develop irregular pseudowhorls of branches that originate within the terminal bud by syllepsis, their extension coincident with that of the parent axis. The two kinds of axes show considerable anatomical differences, but are still based on the common feature of a single stelar-derived trace to each leaf that becomes subdivided in the cortex, a feature of the whole family. Trunk axes include extended cortical leaf and branch traces associated with abundant sclerenchyma, but branches have short cortical leaf traces, no branch traces, and limited sclerenchyma. Reiteration is limited and largely involves the formation of basal suckers on the trunk. Branches normally remain unbranched, but can do so most often when damaged. This study thus emphasizes the phenomenon of axis differentiation in conifers, which has been little investigated anatomically, but could be very important in the identification of fossils.

Key Words: Araucariaceae • Massart’s model • orthotropy • plagiotropy • shoot morphology • vascular anatomy • Wollemia nobilis

Received for publication 18 November 2008. Accepted for publication 19 June 2009.

FOOTNOTES

¹ Research was supported by the Eleanor Crum Professorship in Tropical Botany of the National Tropical Botanical Garden. The authors thank the Director and J. B. Fisher, Fairchild Tropical Botanical Garden for part-time use of research facilities at The Center for Tropical Plant Conservation and C. J. Quinn for photographs and open-grown material from the Royal Botanic Gardens, Sydney, Australia.

⁵ Author for correspondence (e-mail: pbtomlin{at}fas.harvard.edu)

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