Rio Grande Greenthread

Distinctions between Thelesperma nuecense and T. filifolium are subtle; they may be better treated as one species.

Annuals, 30–70(–90+) cm. Cauline leaves ± scattered over proximal ¹/4–¹/2(–³/4) of plant heights, inter­nodes mostly 4–10 cm; lobes mostly linear to filiform, sometimes ± oblong, 25–50(–120) × 0.5–1+ mm. Calyculi of 6–7+ narrowly triangular bractlets 2–4 mm. Ray florets 8; laminae yellow to golden, usually proximally, sometimes almost wholly, suffused with red-brown or with a red-brown spot or band, 10–20+ mm. Disc corollas red-brown, throats shorter than lobes. Cypselae 5–5.5+ mm; pappi 0.5–1+ mm. 2n = 20.