For any uninitiated readers, here is a quick note about keys for identification. Keys are series of binary choices that when completed lead to identification of a plant. In a species key for Lycopus in Michigan, the first choice is sepals more or less than one milimeter. The next choice is if the nutlets are knobby or smooth at the top. Finally, the forward edge of the leaf teeth are either perpendicular to the axis or at an acute angle. This last choice determines whether you have the previously posted L. americanus, or L. europaeus. I'm mentioning this process for these two species because their general appearance is very similar. Without attention to these particular details, good identifications would be hard to make. Other variations between the species are not as reliable. For instance, the American species is generally more smooth than the European one. But there is a variety that is actually hairier than its European relative. Keys to Michigan plants, and therefore most midwestern ones, can be found online at http://michiganflora.net/. Those for many plants of North America north of Mexico are at http://www.efloras.org/flora_page.aspx?flora_id=1. This site is about 2/3 complete.