I wondered if the not-quite-right appearance of the leaves might relate to whatever caused the demise of the main tree. If it had a disease or nutritional issue for example then perhaps that could affect the sucker growth if that's what it is. It would be helpful to take a spade to it and see if the base of any shoots are attached to the stump but the municipality would take a dim view of that most likely
According to my field guide there is no other genus of trees in North America with opposite palmately compound leaves. So if not Aesculus that would mean it's either not a tree or it's some more unusual alien.
Presumably there are other street trees on that road? If so, what are they because cities don't often plant a different tree at each spot?
If it's not a tree then back to Rodgersia, which likes light shade and soil on the moist side which I'm thinking would be unusual in a street, but it's got to be something!
