Serviceberry, Saskatoon, Shadbush, Juneberry, Sarvis-tree, Snowy Mespilus, ... Strangely, this seems to be one family where the confusion surrounding common names is exceeded by the uncertainty associated with species identification. I am particularly intrigued and confused by the species Amelanchier lamarckii, Which has apparently naturalized in parts of Europe, but which is usually listed as being of eastern North American or unknown origin. Whereas most Amelanchier cultivars I am familiar with definitely tend toward a shrubby habit, the few specimans of lamarckii I have seen seem much more tree like. One, in particular, which I recall from the Washington Park Arboretum (Seattle), I would guess was at least forty feet tall with a large single trunk. Two questions: Is this the typical mature size and habit? Why is this tree not more commonly available in western nurseries?
It is usually shrubby in Britain, but can occasionally grow as a single-stemmed tree; the largest specimens in Britain are (tallest) 13m tall, and (stoutest) 45cm diameter (Tree Register of the British Isles). – D. L. Clarke, in Bean, Trees & Shrubs Hardy in the British Isles, Supplement
Regarding the common names, don't worry about that as there are no correct ones. It doesn't matter if the same ones are used for various species. The botanical names of this genus, on the other hand...authors do not agree what constitutes each species. Some cultivars are on the market under the wrong species (not an occurrence peculiar to this genus). Same Amelanchier species or cultivar can often be purchased in either shrub or tree form, that's usual with these--they grow as either, depending on circumstances. Labeling in Seattle arboretum has some problems, possibly a particular specimen not being like what was expected can be due to it not actually being that particular species or cultivar. Forthcoming second edition of Trees of Seattle will offer some help with this--for those trees that are found both in the arboretum and elsewhere in town. Jacobson went through the entire collection recently. More serviceberry selections are available here than overseas, so the ones they think are best will not be based on general experience with the full range of them.