Unfortunately we can't tell from the photo which species that is, and it sounds like you already found a key like this one that notes the differences between species, so we don't have any other information to share about distinguishing features. For plants occurring wild in Maryland, Virginia Spiderwort (Tradescantia virginiana) is the local native that's found in multiple counties, while Glaucous Spiderwort (Tradescantia ohiensis) has a much more limited distribution and is non-native, at least according to Maryland Biodiversity Project. (According to the Biota of North America Program, T. ohiensis overlaps greatly in native range, though we don't know if they can naturally hybridize.) An experienced member of the Maryland Native Plant Society might be able to help you ID a sample more concretely next season.

Miri