Horkelia sect. Capitatae
in N. L. Britton et al., N. Amer. Fl. 22(7): 7. 1959.
Plants forming tufts or open mats, green or reddish, rarely grayish, conspicuously glandular, resinously aromatic. Stems ascending to erect, (0.6–)1–6(–9) dm. Basal leaves planar; stipules entire; leaflets 3–8(–15) per side, separate, sometimes ± overlapping, divided 1/5–3/4+ to midrib into (3–)5–15 teeth or lobes not restricted to apex. Inflorescences open to ± congested, flowers usually arranged in ± capitate glomerules, arranged individually in H. fusca var. filicoides. Pedicels remaining ± straight, outermost sometimes ± reflexed in congested inflorescences, 1–3(–10) mm. Flowers: epicalyx bractlets linear, 0.2–0.3(–0.5) mm wide, entire; hypanthium interior glabrous; sepals acute to acuminate; petals white to pale pink, often veined with pink to rose, ± oblanceolate to cuneate, apex emarginate to truncate or rounded; filaments white, glabrous, anthers longer than wide; carpels 10–25. Achenes 1–1.8 mm, smooth.
w United States.
Rydberg recognized seven species in his group Capitatae, treated here as intergrading variation within a single species. Plants of the section share the characteristic Horkelia odor, glandularity, and planar leaves of sect. Horkelia, but differ in the combination of relatively small, short-pedicelled flowers that (except for var. filicoides) are most commonly aggregated into one or more capitate, purple-suffused glomerules, with linear epicalyx bractlets, oblanceolate-cuneate petals that are often pink-tinged, and relatively short, broad filaments.