Ask-a-Dave's-Gardener: Help to ID Mystery Plant, 3 by lchrein

lchrein wrote:
Please see the attached images - this is a plant that has been sprouting in our yard on and off for a few years. We simply cannot seem to ID it… We’ve tried local garden centers, the Cornell Cooperative Extension in our area, local farms… no one has any idea what it is.

It appears to be some sort of tropical plant, though we are in New York, on Long Island. It first appeared right after Hurricane Sandy, which brought a number of different plant/weed species to the Island, mostly crabgrass of various kinds.

Please let me know if you have any idea what this may be.