This has a broad lower midwestern range, mostly from Ill. and Mo. to Lou. and e. Tex., especially on calcareous clayey soils. It is also locally common in w. Tenn., Miss. and Ala.. It overlaps in range slightly with the more northeastern biennis, which is often confused, and hybridization has been reported (Raven & Gregory; Cr). G. filiformis is mapped here based only on a few, mostly old colls. from roadsides in CALL, CHRI, ?MCRA, PULA and TRIG (Munz 1965; Raven & Gregory 1972; M). A reported 1850 coll. of "longiflora" by C.W. Short appears to be biennis (LSU). The species is also known from nearby on Fort Campbell and elsewhere in Montgomery Co., Tenn. (APSC). G. filiformis differs from typical biennis in its stems, usually strigulose on distal internodes with dense ascending hairs (versus villous with more spreading hairs); there are also spreading glandular hairs in the inflorescences of some populations (e.g. Munz's var. kearneyi), but in biennis such hairs are predominant and stigulose hairs are lacking. Also, filiformis has rather stiffly erect inflorescence branches (versus more long-flexuous), with plants usually reaching 1.5-4 m in height (versus 1-2 m); stems dry to a relatively pale or mottled brown to reddish (versus more uniform, darker purplish). Leaves are mostly smaller (the larger ones ca. 10-15 mm wide versus 15-25 mm), and they dry to a pale, greyish green color (versus darker, orange-brownish green). Fruits have 2-4 seeds, and often sharp angles (versus 3-6 seeds and consistently rounded angles). See also notes under filipes, which has been sometimes confused.