U. grandiflora and U. perfoliata have pierced leaves. The following two species do not. U. sessifolia , the sessile-leaved bellwort, has more slender stems and leaves. As the name implies, the leaves have no stalks, but are clasped to the stems. The foliage has a yellowish background with green veins.
Flowers are a pale-yellow or straw color.
After the blooms have been pollinated, look for small, triangular, pods in a pale green. This species also has the distinction of being a runner, spreading by stolons. While I have had all three of the above species in my garden for some years, I have yet to see this species show up in a native plant catalog. Needless to say, if you have a source, or have plants in your garden for trade, I would appreciate hearing from you. This species is very similar to U. sessile in general appearance, with the exception of the leaves being shinny green on both sides.