Square weed (buttonweed, oval leaf false buttonweed, borreria)
Spermacoce latifolia

Annual or perennial herbs or small subshrubs; stems prostrate or erect, usually 4-angled, glabrous to hispid or scabrid. Leaves opposite or pseudo whorled, usually lanceolate to ovate or elliptic, sessile or petiolate, stipules adnate to petioles, forming a sheath, margins with 1 to numerous filiform setae. Flowers usually small, perfect, sessile, in axillary or terminal, usually many-flowered clusters subtended by 1-2 or more pairs of bract-like leaves, stipule-derived bracteoles with setae; hypanthium obovoid, turbinate, or sometimes with intermediate teeth; corolla funnelform or salverform, the tube usually very slender, the lobes.