8c. Xanthisma spinulosum (Pursh) D. R. Morgan & R. L. Hartman var. glaberrimum (Rydberg) D. R. Morgan & R. L. Hartman, Sida. 20: 1408. 2003.
Sideranthus glaberrimus Rydberg, Bull. Torrey Bot. Club 27: 621. 1900; Haplopappus spinulosus (Pursh) de Candolle subsp. glaberrimus (Rydberg) H. M. Hall; H. spinulosus var. glaberrimus (Rydberg) S. F. Blake; Machaeranthera pinnatifida (Hooker) Shinners var. glaberrima (Rydberg) B. L. Turner & R. L. Hartman; Xanthisma glaberrimum (Rydberg) G. L. Nesom & O’Kennon
Perennials, 20–50 cm, often woody at base. Stems stiffly erect, branched in distal 1 / 3 ; mid internodes 2–5 mm. Leaves numerous, strictly ascending, not reduced distally, margins pinnatifid, lobes oblong-lanceolate to triangular, 2–7 mm, faces usually glabrous, sometimes lightly tomentose, eglandular. Heads 2–10+, (subsesssile) usually clustered. Peduncles relatively terminal and lateral, 0.5–2 cm. Involucres 8–15 mm wide. 2n = 8, 16.
Flowering spring–fall. Sandy to gravelly prairies, hillsides, and roadsides; 800–1400 m; Colo., Iowa, Kan., Nebr., N.Mex., N.Dak., Okla., Tex., Wyo.
G. L. Nesom (2003) recognized Xanthisma spinulosum var. glaberrium at species level, as it occurs sympatrically with variety spinulosum in the Texas panhandle, where the two taxa behave like biological species; on the eastern plains of Colorado, however, hybridization and autoploidy have been documented (D. P. Hauber 1986).
