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Thlaspi alliaceum L. (Brassicaceae) is a weedy, annual, European species of ruderal habitats known from 14 states in the eastern USA. It first was collected in North America in 1947 in Pennsylvania, although most references cite a 1956 collection from North Carolina. The species now has been vouchered in 23 Pennsylvania counties. Populations frequently consist of thousands of individuals. Despite its frequency, Thlaspi alliaceum is underreported in published works on the Pennsylvania flora.

Since their recognition over 20 years ago, knowledge of the distribution and taxonomic affinities of the perennial Vittaria gametophytes found in the eastern United States has expanded greatly. Once thought to be extremely rare and local, they now are known to be common in selected habitats over a broad region of the Appalachians. Farrar (1978) summarized the history of this taxon and presented a map of its distribution as then understood. Vittaria gametophytes have been discovered in the unglaciated Appalachian Plateau, Blue Ridge, Ridge and Valley, and Upland Piedmont provinces, all uplifted bedrock areas which presumably have been in continuous existence since Tertiary times. Farrar et al. (1983) discussed these recent finds and reported the gametophytes from sites in Ohio and Pennsylvania near the limits of Pleistocene glaciation. This article describes the presence of Vittaria gametophytes beyond these limits. This unusual fern now has been discovered on the glaciated Appalachian Plateau nearly 90 km north of the southern limit of Wisconsinan glaciation. This also is the first report of Vittaria gametophytes from the watershed of the Great Lakes.