While we are on the subject of shad trees we might as well take a minute to tackle a subject that has driven many taxonomist to blows. As I am sure you know there are at least 6 species of Amelanchier: A. arborea, A. alnifoilia, A asiatica, A. canadensis, A. laevis and A. stoloniferia. Of those species 3 are fairly common to the eastern part of the country. That would be A. arborea, A. canadensis and A. laevis.
Am I losing you yet? Is this post relevant to me or the lives of my loved ones?
No. This post only matters if you are in the market for a shad tree and even that excuse is tenuous at best. While shopping at the shad store you will quickly notice that almost all the plants are labeled 'Amelanchier canadensis'. I can say with confidence that almost all those labels are wrong. What you are most likely purchasing is 'Amelanchier arborea'. As far as I can tell A. canadensis is not grown on any kind of large commercial scale. According to Dirr (Manuel of Woody Landscape Plants 5th Edition) the confusion is rampant.
Laziness or some misguided marketing ploy? Does 'Amelanchier canadensis' roll of the tongue easier than 'Amelanchier arborea'? At any rate I will revisit Amelanchier in the fall when the plant starts to fruit.