Jolls, Claudia L. .
Hedging our bets: seed mass, morphology and germination of Packera tomentosa.
Different forms of seeds on the same plant, heterocarpy, is presumed to be a form of evolutionary bet-hedging in unpredictable environments. Such differences in seed morphology and behavior are common in members of the Asteraceae, particularly between ray and disk achenes and specifically in the genus Senecio. We have begun investigation into the possibility of heterocarpy in woolly ragwort, Packera tomentosa (Michaux) C. Jeffrey (Senecio tomentosus Michaux), a spring-flowering perennial of shallow soils of the southeastern US. A smaller subset of late-flowering heads from 56 plants was selected for comparison of fruit from outer and inner florets. This data set showed equivalent seed mass of ray and disk achenes but significant differences among plants. Filled achenes were just as liked to be from outer vs. inner florets. We compared morphologies of outer and inner fruits using a FEI Quanta 200 scanning electron microscope on low vacuum mode to view dry achenes. Magnification at 180X of Packera cypselae provided good contrast, suggesting distinctive morphologies between fruits, including possible thicker ridges in the outer achenes. Packera tomentosa does have rows of trichomes and a pappus on the fruit, typical of the heterocarpic S. jacobaea. Germination success of 7-17 mo old lab-stored fruit at 25/15 degrees C 16/8 hr thermo- and photoperiod was poor; moist stratification improved germinability. Our measures of seed morphology, behavior and associated inferences are challenged by significant variation within heads and among plants due to environment, genetics and/or phenology. Some molecular studies place heterocarpic Senecio jacobaea closest to the genus Packera, suggesting we should expect heterocarpy, however, phylogenies are disputed. We do not yet reject the possibility of heterocarpy in Packera tomentosa.
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1 - East Carolina University, Department of Biology, Howell Science Complex, Greenville, North Carolina, 27858-4353, USA
Presentation Type: Oral Paper:Papers for Sections
Location: 552B/Convention Center
Date: Tuesday, August 3rd, 2010
Time: 3:00 PM