How to tell with great certainty if an Acer is platanoides or pseudoplatanus, if we are sure it is one of the two?
Here are the pictures of my five maples' leaves:
First, all together:
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The leafs are different. I recognize the difference between them because the pseudoplatanus usually has red petioles (leaf stalks), and the leaf seems a bit darker then platanoides. The leafs of platanoides also seem to be more 'spiky' compared to pseudoplatanus, like more sharper points, and more points. It (platanoides) looks more like the real Platanus leaf (the tree they were both named after, obviously). I think in your first figure the difference is best depicted.
The other answer is correct - Norway maple leaves do have more spiky bits at the leaf margins and the obvious red petioles. In your own photograph, the Norway maple is on the left and the sycamore on the right, but also, if possible, check the samaras or keys in pairs, not singly. The pairs are held at a more horizontal angle with Norway maple, whereas sycamore samaras droop down either side rather more, which is clearly illustrated in the Mathilde Cinq-Mars illustration you've already displayed.
I use the angle of the helicopter seeds, and the time of flowering:
Acer pseudoplatanus: angle nearly 90 degree and it blooms after growing some leaves.
Acer platanoides: angle more then 90 degrees, but less then 180 degrees, it blooms before the first leaves.
And I have Acer campester which has the angles around 180 degrees, and Acer opalus with angles less then 90 degrees. But such trees are also different in habits and trunks
A quick and easy test, though too late for this year - If you pull a leaf off a maple in late spring or summer and the end of the petiole "bleeds" milk, then it's always Acer platanoides.
In the photo above the seed photo, the left-hand leaf is most likely platanoides (could be saccharum, I suppose, although the cuts between the lobes appear to be too shallow).