ABSTRACT Range extensions to Butler County (Albizia julibrissin Durazz., Maclura pomifera (Raf.) C.K. Schneid., and Magnolia kobus DC.), Mercer County (Bellis perennis L.), Venango County (Lespedeza cuneata (Dum. Cours.) G. Don), and both Allegheny and Lawrence Counties (Arundinaria gigantea (Walter) Muhl.) are reported. All species are nonnative to Pennsylvania, and L. cuneata and A. julibrissin are considered invasive species in the commonwealth. The occurrence of M. kobus from a wet lowland forest in Butler County represents the first naturalized report of the species from the western half of the commonwealth. The reports of A. gigantea from Allegheny and Lawrence Counties are notable because they represent the second known occurrences of naturalized populations in Pennsylvania.
INTRODUCTION Plants that have been artificially introduced to an area outside their native range are referred to as being nonnative species in these introduced regions (USDA, NAL 2016). In some cases, nonnative plants are further classified as invasive species if they cause economic or environmental harm to the ecosystem into which they have been introduced (USDA, NAL 2016). Invasive plant species are well documented as causing major disturbances in ecosystems throughout the USA (Boyce 2010). In Pennsylvania, nearly 90 invasive plant species have been identified (PA DCNR 2015).
During the past decade, we have observed the occurrence of many previously unreported species throughout the northwestern region of Pennsylvania (Chmielewski and Krayesky 2012, 2015; Krayesky and Chmielewski 2014). We question whether these populations represent new occurrences or were simply overlooked species. We offer insights as to why these invasive/nonnative species were previously unreported from their respective counties.