White ash is a polyploid species. Diploids (2n=46) occur throughout the species range but most tetraploids (2n=92) are found south of latitude 35° N and hexaploids (2n=138) are concentrated between latitude 35° and 40° N. Although three ecotypes were previously recognized on the basis of seedling morphology and ploidy level (15), recent work has shown that the variation in several traits is closely related to latitude. This clonal variation and the strong effects of ploidy level on several other traits indicate that ecotypes probably do not exist in white ash (2).
Hybrids White ash and Texas ash (Fraxinus texensis (Gray) Sarg.) intergrade in Texas. The pumpkin ash (Fraxinus profunda (Bush) Bush) behaves in many respects as if it were a true breeding hexaploid derivative of a cross between tetraploid white ash and diploid green ash (Fraxinus pennsylvanica Marsh.). However, attempts have failed to artificially cross the two species. It is likely that natural hybridization between white ash and other species is extremely rare (16).
- Burns, Russell M., and Barbara H. Honkala, technical coordinators. 1990. Silvics of North America: 1. Conifers; 2. Hardwoods. Agriculture Handbook 654 (Supersedes Agriculture Handbook 271,Silvics of Forest Trees of the United States, 1965). U.S. Department of Agriculture, Forest Service, Washington, DC. vol.2, 877 pp. http://www.na.fs.fed.us/spfo/pubs/silvics_manual/table_of_contents.htm
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