Annuals, 5-85 cm (herbage glabrous); taprooted (roots deep, slender to thick). Stems usually 1, erect, simple proximally, branched distally, glabrous. Leaves cauline (opposite proximally); ± sessile; blades linear to filiform, margins entire. Heads borne singly. Peduncles not inflated distally, usually bracteate. Calyculi of 8, ovate to lanceolate bractlets. Involucres narrowly cylindric, 4-5 mm diam. Phyllaries 8 in 1-2 series, linear, margins scarious, apices acute (keeled). Receptacles flat, pitted, glabrous, epaleate. Florets 8-11; corollas pale purple or lavender, with white-tips. Cypselae pale green or tan, subcylindric to ± fusiform, apices abruptly constricted, not beaked, ribs 8-10, scabrous distally; pappi of 30-50, basally connate, white, ± equal, smooth or barbellulate bristles in ± 1 series. x = 6.
Shinnersoseris rostrata was included in Lygodesmia; Tomb presented evidence for placing it in a separate genus. It differs from Lygodesmia in having opposite proximal leaves, shorter, obscure ligules, shorter style branches, 8-10-ribbed cypselae, echinate pollen, and a different base chromosome number (x = 9 in Lygodesmia.)
This project was made possible in part by the Institute of Museum and Library Services [MG-70-19-0057-19].