This is a widespread, highly variable species, centered largely in the midwest; 2n = ?18-36 (Cr, FNA 23). It may hybridize locally with tenuis, bifida, elliptica and erythropoda. Several records from Ky. remain uncertain; see also notes under bifida. At least one coll. from LEWI (KNK, R.F.C. Naczi #3811) may be transitional to typical elliptica; it was det. by G. Smith as "compressa x elliptica probably."