This alien is reportedly widespread in North America, usually growing in pavement crevices, roadside margins and similar places (FNA 5, PL). There has only been a provisional review of colls. from Ky. in the aviculare complex, but arenastrum undoubtedly occurs throughout the state. Colls. mapped here as uncertain records have relatively narrow leaves, suggesting bellardii, but may just be forms of arenastrum. Compared to typical aviculare, seeds of arenastrum are usually 1.5-2.7 mm long (versus 2.7-3.7 mm); flower length is usually 2-3.4 mm (versus 2.8-4.7 mm), with ca. 40-60% as the tube (versus 20-40%); leaves are relatively uniform in size (with early leaves only ca. 0.5-2 cm long versus up to 2.5-6 cm in aviculare) and bluish-green (versus plain green). It is prostrate to ascending (versus ascending to erect), with stems mostly 1-5 dm long (versus 2.5-7.5 dm).