Developmental and Structural Section
Richards, J.H. , Troxler-Gann, T. , Dow, M.H. , Lee, D.W. .
Morphology and growth of Nymphoides aquatica (Menyanthaceae) in response to water depth.
The big floating heart (Nymphoides aquatica) is a common component of southern Florida Everglades sloughs and long hydroperiod marshes. The species reproduces primarily by vegetative propagules that are produced below the cordate laminae of the floating peltate leaves. Developing propagules first produce the cymose inflorescence, then swollen adventitious roots below the inflorescence, then a vegetative apex that can produce a new shoot. As a leaf senesces, this reproductive unit breaks from the parent plant below the inflorescence, floating at the water surface until it settles and roots. Not all floating leaves have propagules and not all propagules expand flowers. In an ongoing mesocosm experiment examining responses of Everglades slough species to water depth and hydroperiod, we have documented growth of N. aquatica in response to water depth. Plants collected from a southern Florida slough were grown outside in pots submerged to depths of 30, 60 or 90 cm in nine 3410 L mesocosms; each mesocosm had three N. aquatica plants at each depth. Morphological characters were measured monthly from Jan. 2006 until Jan. 2007. Thirty-seven percent of the plants died during the year. Mortality was greatest (26%) in plants growing at 90 cm, followed by plants in 60 cm (11%); none of the plants in shallow water died after the establishment phase. Although N. aquatica plants produced axillary buds on the submerged rhizome, fewer than 2% formed vegetative rhizome branches. Plants in deeper water produced fewer leaves per month than plants in shallow water, but these leaves had longer petioles and larger laminae. Season affected lamina size, with larger laminae produced in warmer months, but petiole length did not vary seasonally. The data suggest that although N. aquatica can grow under deep slough conditions in southern Florida, growth and survival are better in shallower water.
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1 - Florida International University, Dept. of Biological Sciences, 11200 SW 8th St., Miami, FL, 33199, USA
Presentation Type: Oral Paper:Papers for Sections
Location: PDR 2/Hilton
Date: Monday, July 9th, 2007
Time: 9:00 AM