Yeah, it looks like the samaras were shed. Sometimes one windy day can carry them everywhere. They can hybridize. As Dax said, it is probably black maple. Black and Sugar can hybridize easily, and in fact, it's sometimes thought that the Sugar Maple cultivar 'Green Mountain' is actually a hybrid of black and sugar, but I don't think that has ever been proven. Sugar Maple, I believe can hybridize with any of the other "sugar-type" maples: Acer nigrum (Black Maple) Acer grandidentatum (Bigtooth Maple) Acer leucoderme (Chalk Maple) Acer floridanum (AKA Acer barbatum) Florida Maple or Southern Sugar Maple Acer skutchii (Mexican sugar maple) I don't know if it can hybridize with others, but I'm pretty sure it cannot hybridize with the other common Eastern maples, at least not the commonly found large ones (Red and Silver). I don't know if they're pollen-compatible, but the bloom times don't overlap, so it at least won't happen in nature. I also don't believe it can cross with Norway Maple (Acer platanoides), despite their superficial similarities, they're actually not that closely related. There may be some Asian maples they could cross with, but I'm not sure. Someone more knowledgeable can chime in I'm sure.

Everything GG has said I agree with... my dissectums have little seed if any ever.... and there is no reason seeds should be expensive but for the ignorance of the general public who are willing to pay for a named cultivar seed that most likely won't look like the named cultivar...but I do understand the ignorance since i use to believe 6 years ago there were just two japanaese maples ... "regular" and "lace leaf" and I might have bought into the seed thing if I saw them advertized!!! I bought plain atro's for much more than I should have...you are only the sum of your knowledge, experience, and ignorance ;>)For MOST folks doing seeds is not smart unless you have unlimited space and want to experiment with hundreds of seedlings...same goes with grafting unless you really want to "get into it " to graft for one or two trees is rediculous IMHO....And doing cuttings is iffy as GG said most will tell you you should wait two seasons to be sure they actually will survive. No... the best way is to buy a named cultivar from a reputable dealer local or internet if you just want a couple of trees for a particular spot or as i said you have lots of land , time, and like to just play around and experiment David

With respect to Japanese maples specifically it is not a question of the age of the tree itself but rather of the age of the grafted stock. Even very small/young JM's can produce flowers and seeds, as the grafted portion is typically obtained from fairly mature stock. FWIW, flowering and seed production of JM's can be very sporadic - some cultivars tend to flower very freely, others not so much. It can also be influenced by growing conditions.

Interesting, the publication by Wright also shows hybrids with Acer platanoides (Norway maple) and Acer negundo (Boxelder maple), as well as Acer saccharinum (Silver maple) and Acer negundo (Boxelder maple). It would be interesting to see such a study replicated, and for a full growth cycle for the hybrids to take place. I live in Utah, and the native Acer grandidentatum (Bigtooth maple, close sugar maple relative) flowers at the same time as the invasive non-native Norway maple in our foothills at about 4,500 ft. Sometimes bees cross-polinate them, I'm sure of it when both trees grow near. Bees still prefer the Norway maple for its showy and nectar rich flowers. Both insects and wind pollinate them, but mostly wind because sometimes it is too cold for bees to work. I have grown some potential hybrids between the Norway and Bigtooth maple, from a Bigtooth maple 'female' tree, and the seedlings were weak, waxy/glossy, and lime green possibly from iron chlorosis. None of those made it after a week...