Developmental and Structural Section
Seago, James .
Anatomy of Trapa natans and Justicia americana in riverine habitats.
Upstream from the Minetto dam on the Oswego River, New York, 8 K from Lake Ontario, two eudicot species have become conspicuous inhabitants of the river during the past decade. Floating, rooted plantlets of Trapa natans extend from their submersed fruits to cover standing, near-shore waters; substrate-rooted plants of Justicia americana emerge from their rhizomes along the shore among other, mostly monocot emergents. These eudicot species were investigated to determine their root and shoot anatomical characteristics that allow them to be adapted to their different riverine habitats. Aquatic and substrate-anchored adventitious roots of Trapa have a cortex with expansigenous aerenchyma, an endodermis with Casparian bands, and an exodermis with Casparian bands and suberin lamellae; the stele is triarch to pentrarch with primary growth. The hypocotyl has a central stele and small, expansigenous cortical aerenchyma, and it differs from the stem which has very large lacunae; the stele lacks secondary growth, but is surrounded by an endodermis. The fan-shaped floating leaves have petioles with inflated regions of enlarged aerenchymatous lacunae and characteristic blades with very large air spaces in spongy mesophyll. Adventitious roots of Justicia develop early secondary growth with considerable xylem and little phloem, and an endodermis with Casparian bands redivides to keep pace with stele expansion. The cortex has mostly schizogenous aerenchyma and is bounded externally by an exodermis. Rhizomes and stems below water level have an endodermis with Casparian bands around individual vascular bundles, considerable secondary tissue within the limits of the bundles, and limited schizogenous-lysigenous aerencyhma, while stems above water have no endodermis and less secondary growth. The epidermis is underlain by a hypodermis and layers of collenchyma in the outer cortex.
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1 - State University of New York, Biological Sciences, Oswego, NY, 13126, USA
Presentation Type: Oral Paper:Papers for Sections
Location: PDR 2/Hilton
Date: Monday, July 9th, 2007
Time: 8:45 AM