I noticed these volunteers in a majesty palm that spent last summer on the patio under an ash tree, so at first I thought they were ash volunteers, but when I later potted up some "legitimate" ash seedlings from the yard I noticed that these guys look very different... and just last night I noticed they are photo-sensitive, leaves all curled upward in the darkness. (They've been growing indoors for 4 months now). Could these be mimosa??? My 2nd guess is some form of acacia or honey locust but I don't know if these are sensitive to light or not. I suspect these either came in with the palm's potting medium, or perhaps in the bit of sea soil I added when I transplanted the palm. Thank you in advance!
Safe to exclude Mimosa, as that has much narrower leaflets (e.g. pic here). More like a Robinia; that usually has opposite leaflets (pic), but it can occasionally show alternate leaflets (pic) like your plant has.
