Annuals (sometimes persisting), 10-40(-70+) cm. Cauline leaves crowded to ± scattered over proximal 1/2-3/4 of plant heights, internodes mostly 10-35(-50+) mm; lobes mostly linear to filiform, sometimes oblanceolate, 5-30(-55+) × 0.5-1(-3+) mm. Calyculi of 7-8+ linear to narrowly triangular bractlets (2-)4-8+ mm. Ray florets 8; laminae yellow to golden yellow (sometimes proximally suffused with red-brown), 12-20+ mm. Disc corollas red-brown or yellow with red-brown nerves, throats shorter than lobes. Cypselae 3.5-4+ mm; pappi 0.5-1(-2+) mm. 2n = 16, 18.
Flowering Mar-Aug(-Oct). Disturbed sites on clays or sandy soils, rocky slopes, often on limestone; 10-2200 m; Ark., Colo., Kans., La., Miss., Mo., Nebr., N.Mex., Okla., S.Dak., Tex., Wyo.; Mexico (Nuevo León).
As here circumscribed, Thelesperma filifolium includes plants that others have treated as a distinct species or variety: T. intermedium or T. filifolium var. intermedium, characterized as plants mostly 10-40 cm (versus taller); internodes 'relatively short' (versus longer); calyculus bractlets mostly 1/4-1/2 lengths of phyllaries (versus more than 1/2 as long); ray corollas yellow (versus 'golden yellow'); disc corollas yellow (versus sometimes red-brown); distribution mostly north and west of the typical form (Colorado, Kansas, Nebraska, New Mexico, w Oklahoma, South Dakota, c and w Texas, Wyoming).
According to A. Cronquist (1980), Thelesperma trifidum (Poiret) Britton has been misapplied (e.g., M. L. Fernald 1950) to T. filifolium.