All four species are natives of Europe, the two large flowered species sometimes cultivated 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; leaves all green.

L. album

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, leaves with a white streak along the midvein. 

L. maculatum

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).

L. amplexicaule

3. Leaves subtending flowers short-petioled, reflexed, the blade about as long as broad or a little longer.

L. purpureum