Acting as “weed” in my yard. Unusual flower/seed arrangement on back of rachis(?). Leaflets not touch sensitive, but closed moments after stem was cut. Alternate leaves, leaflets also alternate.
it does look like a sensitive plant, but it is actually in the spurge family, Euphorbiaceae. It appears to be Phyllanthus amarus, an introduced species, similar to our native Phyllanthus caroliniensis which does not become weedy. The ‘leaves’ are actually branches with many leaves, each of which has a tiny flower under it which develops into these tiny fruits. An interesting plant, though weedy.
Steven Hill, Ph.D. Botanist SCNPS