Non-native plants observed in North America by 18^th century naturalists

Writings of 18th century naturalists provide a rich description of the flora, agricultural practices, and ecological and cultural landscape during the migration of large numbers of European and African peoples to North America. We employed a mixed methods approach to: 1) compare the percentages of non-native vs. native plant species recorded by the naturalists; 2) quantify the relative frequency of non-native plant species across eastern North America; and 3) qualitatively evaluate descriptions of non-native plants. The writings from nine naturalists in the 1700s document the introduction and establishment of many non-native plants across the North America. Higher proportions of non-native plant species were reported by naturalists who spent more time in densely populated human settlements. Agricultural crops had the highest relative frequencies for non-native plants in the 18th century. Non-native plants were described as being used during daily activities by humans, undergoing cultivation, growing abundantly on the landscape, and having weedy growth characteristics. Several of the non-native plants observed in the 1700s have subsequently developed into invasive species, which threaten the conservation of native North American flora.