Eight populations of Amelanchier growing in the Delaware River valley regions of New Jersey and Pennsylvania were analyzed, using the techniques of the hybrid index. No barriers to hybridization were found in the populations of A. arborea and A. laevis, and of A. canadensis and A. laevis, and a complete range of plants intermediate between these two sets of parental extremes were analyzed. These species are homoploid, with 2N = 68. In contrast, no plants were found which are intermediate between A. canadensis and A. arborea on the basis of morphologic characters. Consideration is given to the significance of ecological and temporal barriers to gene flow. The suggestion is made that A. canadensis, A. arborea, and A. laevis be considered as one variable co-specific complex under the earliest valid epithet, A. canadensis (L.) Medic. (1793).
The Fate of Vanadium in an Urban Air Shed: The Lower Delaware River Valley
