This alien annual was first reported in North America ca. 1910, within northeastern regions, but it has now spread through most eastern regions (FNA 5). It has been confused with another East Asian species, P. posumbu (Buchanan-Hamilton ex D. Don) H. Gross (= P. cespitosa (Blume) Nakai), which is unknown in North America; 2n = 40 in both taxa (Kim et al. 2008). The correct author citation has been unclear (K, W). Leaves often have faint to dark marks on leaves, although generally less pronounced than in maculosa, marks are not lacking completely as has been indicated by W.