Little, Stefan A. , Stockey, Ruth A. .
A morphogenetic study of submerged roots and a new type of aquatic bark system (rhytidome) in Decodon allenbyensis from the Middle Eocene Princeton Chert.
Aerenchyma is a well known primary tissue in numerous aquatic plant species. However, less well known, are the aerenchymatous tissues of secondary origin, arising from a phellogen, so called "lacunate phellem". Lacunate phellem occurs in several aquatic to semi-aquatic taxa in Lythraceae, Melastomataceae, Onagraceae, Euphorbiaceae, Myrtaceae and Fabaceae. Aquatic primary tissues as well as secondary tissues are known from the submerged axes of the fossil plant Decodon allenbyensis Cevallos-Ferriz et Stockey, from the Middle Eocene Princeton Chert. Recent investigations have shown these roots connected to exceptionally large woody axes, some with up to 18 growth increments. These large axes possess a distinct pattern of secondary tissues arising from a phellogen system. Alternating bands of "phelloids" and bands of non-active phloem with lacunae compose the tissues of this aquatic bark system. This sort of lacunate phloem and aquatic rhytidome are currently unknown in any living or fossil taxa. A detailed morphogenetic sequence showing the transition from young submerged roots with delicate primary tissues to larger woody axes with lacunate phellem and wood has been documented. The morphogenetic sequence contrasts with that seen in species of Onagraceae (e.g. Ludwigia L.). Morphogenesis in these aquatic roots is now known to a degree that rivals that for most extant taxa, and contributes a number of detailed characters to the whole-plant concept of D. allenbyensis at Princeton.
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1 - University of Alberta, Department of Biological Sciences, Biological Sciences Centre, Cw 405, Edmonton, Alberta, T6G 2E9, Canada
Decodon, Eocene, Rhytidome, phellem .
Presentation Type: Oral Paper
Location: Salon G - Austin Grand Ballroom/Hilton
Date: Tuesday, August 16th, 2005
Time: 2:30 PM