All four species are natives of Europe, two of them known in cultivation and the other two weeds.
1. Corolla ca. 19–26 mm long, the tube curved upward; plants perennial; leaves acute and all petioled.
2. Corolla white, the upper lip ciliate with long hairs (at least 0.5 mm) and usually pilose above as well; terminal tooth of largest cauline leaves prolonged or ± acuminate, often 9 mm or more long.
2. Corolla pink to purplish [albinos rare], the upper lip with hairs less than 0.5 mm; terminal tooth of largest cauline leaves less than 9 mm long.
1. Corolla ca. 9–19 mm long, the tube straight; plants annual; leaves acute to rounded in outline, all or only the lower ones petioled.
3. Leaves subtending flowers sessile, ascending or at most horizontal, slightly broader than long (± reniform in overall outline).
3. Leaves subtending flowers short-petioled, reflexed, the blade about as long as broad or a little longer.
All species found in Lamium
MICHIGAN FLORA ONLINE. A. A. Reznicek, E. G. Voss, & B. S. Walters. February 2011. University of Michigan. Web. February 23, 2018. http://michiganflora.net/genus.aspx?id=Lamium.