4. Mentzelia decapetala (Pursh) Urban, Ber. Deutsch. Bot. Ges. 10: 263. 1892.
Gumbo-lily, 10-petalled western star Gumbo-lily, 10-petalled western star
Bartonia decapetala Pursh, Bot. Mag. 36: plate 1487. 1812
Plants biennial or perennial, bushlike, perennials with ground-level caudices. Stems solitary, erect, straight; branches distal or along entire stem, proximal or distal longest, antrorse, straight to upcurved; hairy. Leaves: blade 72–295 × 14–45 mm, widest intersinus distance 10.1–23.3 mm; proximal oblanceolate or elliptic, margins serrate to pinnate, teeth or lobes 16–26, slightly antrorse, 1–16.5 mm; distal elliptic to lanceolate, base clasping or not, margins serrate to pinnate, teeth or lobes 9–20, slightly antrorse, 5.3–13.7 mm; surfaces with needlelike trichomes. Bracts: margins pinnate. Flowers: petals white, 47–75 × 13–22.7 mm, apex acute to attenuate, glabrous abaxially; stamens white to yellow, 5 outermost petaloid, filaments spatulate, strongly clawed, 48–75 × 12–23 mm, without anthers, second whorl with anthers; anthers straight after dehiscence, epidermis smooth; styles 36–53 mm. Capsules cylindric, 30–43 × 12–17 mm, base tapering, not longitudinally ridged. Seeds 2.3–4 mm; coat anticlinal cell walls straight, papillae 4–10 per cell. 2n = 22.
Flowering Jun–Aug(–Oct). Rock outcrops, slopes, dry short-grass prairies, riverbanks, roadsides, loam, limestone, sandy, silty, clayey, and gravelly soils; 300–2400 m; Alta., Man., Sask.; Colo., Ill., Iowa, Kans., Minn., Mont., Nebr., N.Mex., Okla., S.Dak., Tex., Utah, Wyo.
Mentzelia decapetala is introduced in Grundy County, Illinois. It appears to be native throughout the rest of its distribution.