These have more differences between them than are recognized within red maple. For the most part, if you've seen one red maple you've seen them all - it's pretty uniform, apart from fall leaf color variations etc.

Most people think science is always definitive, and expect to get a definite answer. That is not always the case. We know far more about cholesterol now than we did in the 70's, when the mantra was avoid all cholesterol. Now we know there are beneficial as well as much more harmful forms. However most people do not realize this is because of the learning and correction process has continued and still continues. As for the trees in your example, there is the added complication that the classification into species is purely artificial. The plants don't care. Plus speciation is a process that can go either way at a particular time. Therefore the "lines" are not always clear cut, as in the case of the Sugar Maple group. Often the answer you will get as to their species status will depend upon who you ask. Some will be "lumpers" and lump them all together into a single species with sub-species. Others will be "splitters" and consider them all as distinct species. For our purposes, use whichever you prefer, although considering them separate species could help with identification in the nursery trade. And FYI, a similar circumstance exist for many redbuds.

Arktrees

I did see a tree this weekend at the Maryland Zoo. I snapped a pic on my smartphone but it didn't turn out very clear.

The leaves are sugar-maple like, but slightly smaller. The samaras are a tad larger than an A. saccharum, and slightly wider of an angle, but nothing near A. platanoides.

The tree is smallish, but not particularly young. Almost looks like an A. campestre but again, the leaves and samaras are wrong.

Any guesses?