Japanese maple from Korean nursery-grown stock. From Walter Pall's Bonsai Adventures blog. The two smaller trees exaggerate the effect of the main tree.
Back in the mid-to-late 20th century, when the average person had no idea what the art of bonsai was, almost all bonsai in the U.S. were from landscaping nursery stock. Most were in early stages of development and most never got beyond those early stages (it was a slaughter).
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The three tree maple grove above is also from nursery stock, though no doubt nursery stock grown for bonsai, rather than nursery stock grown for landscaping. It’s an important distinction, though if you’re lucky you might find landscaping stock with good bonsai potential.
This shot gives a good idea of the planting's size. It's one of many shots that take us through refinement and repotting.