Wollemia nobilis: Modern Studies of an Ancient Plant
Tomlinson, P. Barry .
Wollemia nobilis: architecture and vasculature, a comparative approach.
All three genera of the Araucariaceae (Agathis, Araucaria, Wollemia) conform quite precisely to Massartís model in the Hall√©-Oldeman system because of their rhythmic growth and constant distinction between orthotropic (trunk axes) with radial symmetry and plagiotropic (branch) axes with dorsiventral symmetry. A branching peculiarity shared by all genera is that plagiotropic branches originate by syllepsis within the terminal bud of the orthotropic shoot but they do not grow out until extension growth begins. However, in Wollemia the two kinds of axis differ consistently in their phyllotaxis; spiral in the trunk and decussate in the branch, the latter with secondary leaf orientation producing dorsiventrality. The vascular insertion of the branch axis is narrow, Vasculature of leaves is the same in all genera with a single leaf trace (as in all conifers), but distinctive in this family because it branchesg extensively as it passes through the cortex, to result in a leaf (whether scale or foliage) with many vascular bundles. This is consistent in both types of axis in Wollemia despite the discordant phyllotactic patterns. Reiteration in all genera is the same and, in the absence of reserve buds, proceeds from minute axillary (detached) meristems. Reiterated axes repeat the morphology of their parent axis. The same process is theoretically possible following terminal formation of cones and could result in a sympodium, unusual for conifers. These results should eventually extend to a study of mature trees.
Log in to add this item to your schedule
1 - National Tropical Botanical Garden, The Kampong, Coconut Grove, Florida, 33133, USA
Presentation Type: Symposium or Colloquium Presentation
Date: Monday, July 28th, 2008
Time: 10:15 AM