Hemlock and Cow Parsley
This image shows Cow Parsley (Anthricus sylvestris) on the left and Hemlock (Conium maculatum) on the righ. Both plants can grow to be several feet high and at first glance, they look similar. The stems are the first part to examine. The stem on cow parsley is grooved. The stem on hemlock is not and, more importantly, has red blotches on it.
