What is the one characteristic that distinguishes the plant Queen Anne's Lace from a similar harmless plant?

Question

Queen Anne's Lace is a naturally occuring weed in temperate parts of the U.S.

Answer 1

Queen annes lace ( daucus carota) has a single dark flower in the center of the umbel.Poison hemlock and water hemlock do not have this characteristic.

Answer 2

There's no one characteristic that distinguishes it from all other plants, and many people use that same common name for several different species. I assume you're talking about wild carrot, Daucus carota. Two very distinguishing features are the broad umbel with conspicuous bracts, and the fat whitish taproot that smells like...carrot!
Water hemlock has a hollow chambered root, and most other species in the carrot family with dissected leaves have smaller umbels or lack hairs.

Answer 3

I don't understand your question, since Queen Anne's Lace is harmless as compared to the Water Hemlock (which is the more dangerous plant). The root of QAL is a Carrot in fact our normal variety of carrots were derived from QAL. Although the roots are edible, its upper portions can irritate our skin though.

So are you trying to distinguish QAL (1st ref) from a conventional carrot or distinguishing it from Water Hemlock (2nd ref)?