The genus Bartonia, part of the gentian family, is comprised of only three species, two of which – B. virginica and B. paniculata – are native to Pennsylvania.  Our Bartonias are found in wetlands, including fens, bogs, and damp woods, and present tiny white flowers that remain closed for the majority of their blooming periods, which can last from July to September, depending on their location.

Although inconspicuous, the “scale-like” leaves of our Bartonias are an important factor in determining which species is being observed: on B. virginica they are generally opposite, while on B. paniculata they are generally alternate.  One thing that all Bartonias share in common is their diminutive size – plants are usually only a few inches tall (although some can rarely reach as high as a foot) and are easily hidden by surrounding vegetation.  They do, however, tend to prefer dryer, raised hummocks as opposed to wet depressions, which can narrow the search somewhat.

B. virginica and B. paniculata have largely overlapping ranges – both are found across the Eastern U.S. from New England and the Great Lakes south into Florida. However, B. virginica tends to be more common, especially in the Northeast. This generalization extends to Pennsylvania, where B. virginica records exist from most counties, whereas B. paniculata appears to be limited to scattered populations mostly in eastern and northcentral PA and is thus listed as vulnerable in the state.

Sources:

"Twining Screwstem (Bartonia paniculata)." Wisconsin Department of Natural Resources.  See Twining screwstem

"Bartonia paniculata." Pennsylvania Natural Heritage Program. See Bartonia paniculata