Yes, Norway maples are invasive in many areas of the country and should probably not be your first choice. It is also quite likely that the seed from the globe form (Acer platanoides 'Globosum') will not come to true to type - that is, it may very well look more like the straight species.

In fact, growing just about any tree from seed will not necessarily produce the intended results unless that tree naturally has that wide, spreading umbrella-like habit. And most that do are selected from various oddities or sports for that attribute and are then typically propagated asexually (not from seed).

Zelkova may come close to the look you are after.

For a similar amount of contrast between the top and the trunk the closest things would be other grafts of shrubby variants of otherwise normal trees onto straight trunks produced by typical seedlings such as 'Nana' catalpas and 'Umbraculifera' black locusts. In other words, to get that mushroom look you may just have to shell out for a grafted nursery specimen. Few, if any trees on the market produce that same combination of a straight, stout trunk and small, dense, dome-like head as the result of normal seedling growth - it really isn't possible for a comparatively small (within the context of tree sizes), dense bush to generate the trunk of a large, vigorous tree.

This post was edited by bboy on Mon, Oct 13, 14 at 19:07