Developmental and Structural Section
Gibson, J. Phil , Engel, E. Cayenne .
Comparison of germination and pericarp characteristics between homocarpic and heterocarpic species of Grindelia (Asteraceae).
Heterocarpy is a reproductive system in which different flowers on the same plant produce fruits that are structurally and ecologically dissimilar. Homocarpy, in contrast, is characterized by all flowers producing fruits that are structurally and functionally similar. By partitioning offspring among two or more ecologically divergent groups, heterocarpic species reduce risks of environmental heterogeneity on seedling establishment because the differing structural, dispersal, and dormancy traits among fruit morphs counterbalance contrasting spatial and temporal dispersal risks. Hetrocarpy has evolved independently in several plant families, but it is particularly common in the Asteraceae (sunflower family). While numerous studies have investigated the ecology of heterocarpy, no studies have compared them to their homocarpic relatives. We compared structural and functional characteristics of fruits (achenes) produced by heterocarpic and homocarpic species in the genus Grindelia (gumweeds). Our analyses identified structural characteristics of the pericarp that relate to differences in germination and imbibition within and among species. The results of these studies indicate that evolution of heterocarpy not only involves modification of achene morphology, but that modifications of resource allocation patterns between seed and pericarp, and structural modifications of the pericarp are also important components of this reproductive system. Comparisons of homocarpic and heterocarpic species identify potential developmental and structural antecedents that may dictate the evolution of heterocarpy.
1 - Agnes Scott College, Biological Sciences, 141 E. College Ave., Decatur, Georgia, 30030
2 - University of Tennessee, Department of Ecology and Evolutionary Biology, 569 Dabney Hall, Knoxville, Tennessee, 37996, USA
Presentation Type: Paper
Location: Alpine A (Snowbird Center)
Date: Wednesday, August 4th, 2004
Time: 2:30 PM