Submitted to: Systematic Botany
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/30/2003
Publication Date: 6/2/2004
Citation: Whittemore, A.T. Introgression, Genetic Structure, and Taxonomic Status in The Celtis Laevigata. Systematic Botany. Interpretive Summary: The genus Celtis has been identified as a promising candidate for breeding landscape plants that will be tolerant of drought, cold, and poor soils. Currently, very little is known about the taxonomy, genetics and reproductive processes in Celtis. This study investigates genetic structure within one species group where it has often been supposed to be strongly influenced by introgressive hybridization. The data indicates that hybridization is not as frequent in the group as authors have supposed, and that genetic variation in the two species is likely due to high levels of genetic variation and recent common ancestry, rather than a history of introgression. Knowing that interspecific hybridization is not as common in the genus as once believed will help breeds to design breeding work more efficiently, and will also be useful in designing studies to investigate the relationships of Celtis spp., which scientists will also use in designing strategies for Celtis breeding.
Technical Abstract: The North American species of Celtis have been believed on anecdotal grounds to hybridize commonly in nature, and an understanding of the nature and frequency of natural hybridization among species of Celtis is necessary for investigating relationships among Celtis spp. Extensive natural hybridization has been strongly suspected between two species with ranges that overlap broadly in Texas, Celtis laevigata and C. reticulata. Statistical study of morphological and DNA data was undertaken to test the extent and genetic consequences of natural hybridization between them. Results indicate that there is little or no natural hybridization between these species, contradicting past conclusions. The variability and apparent intergradation between the species that led to the hypothesis of introgression is apparently due to high levels of shared genetic variation inherited from a recent common ancestor, plus exceptionally high levels of variation in leaf shape within individual trees.