This is native to sw. U.S.A. and Central America, but occasionally adventive onto the Gulf Coastal Plain (K, W; Weakley et al. 2023). In 2010 it was found by JC along a busy highway in Lexington (FAYE: with Nostoc and cigarette butts along the median of Tates Creek Rd at New Circle Rd); it flowers here from Apr to (in wet years) Jul. Identification has been problematic, with L. ruderale L. (from Europe) initially suggested. But thanks to M. Brock (2020), who has also found the species (2019) on sidewalk in Guthrie (TODD, APSC), we are now confident that oblongum is correct. Recently published keys (including FNA 7 and W) can still be difficult to use in some cases. L. oblongum differs from virginicum and densiflorum in its upper cauline leaves, which are mostly laciniate (versus entire to irregularly dentate); basal leaves are 1- to 2-pinnatifid (versus pinnatifid to dentate); and inflorescence rachises are hirsute with hairs up to 0.3 or reportedly 0.8 mm (versus puberulent with minute trichomes or papillae ca. 0.1 mm long). Also, there are often several stems branching from the base (versus single) and these can be decumbent (versus strictly erect).