Hello, To me, it may also be Acer monspessulanum. Since they're very close species, natural hybrids are very common, it might be a cross between the two species. The leaves may also vary slightly depending of the climate: the drier it is, the smaller the leaves and the fewer lobes. Since neither specis are indigenous to North America (as far as I know), it can be either species. Here are pics of an A. monspessulanum I have in my garden, near Orléans, much more humid and colder than the place it was taken from (Brive-la-Gaillarde, SW France, not Montpellier, F, or Montpelier, Vt USA):
Sorry, no, not Acer monspessulanum; that fairly consistently has 3-lobed leaves, whereas the plant in question clearly shows several leaves with 5 lobes, typical of A. campestre. The shoot bark also differs in appearance. As an aside, A. monspessulanum (Acer sect. Acer ser. Monspessulana) is not closely related to A. campestre (Acer sect. Platanoidea); they are in different sections of the genus. This is most obvious in the seeds (flattened in A. campestre; not flattened in A. monspessulanum) and the sap (milk-white in A. campestre; clear in A. monspessulanum). Claims of hybrids between them are very doubtful indeed.
Very few Montpellier maples are seen here, although as it happens the best site I know of is in Bellingham, WA, comparatively near the Lower Mainland.
After a closer look at the photos, yes, you're right ;) The leaves are not as deeply lobed than the couple I have in pots but these are still very small. They're what I call "birds' seedlings", I salvage them before mowing the lawn, which I have to admit I don't do very often. The matures ones I can see around have slightly more rounded leaves.
