This strict biennial is largely restricted to the Ohio Rv. watershed of east-central states, where it usually occurs on the moist fertile soils of gullies, toe-slopes and terraces. Flowering populations are often small sporadic, but sometimes they are spectacular, with thousands of plants covering several acres. It is generally the only native biennial in its habitat. Synandra is a monotypic genus that is part of a small North American clade that includes Physostegia and a few other genera to the southwest (Scheen et al. 2008).