390. Psilostrophe de Candolle in A. P. de Candolle and A. L. P. de Candolle, Prodr. 7: 261. 1838.
[Greek psilo-, bare, and strophe, turn; perhaps alluding to epaleate receptacles, which differ from paleate receptacles in Parthenium, to which de Candolle compared Psilostrophe]
John L. Strother
Biennials, perennials, subshrubs, or shrubs (rarely flowering first year), 8–60+ cm. Stems erect to spreading, branched from bases or throughout (not scapiform). Leaves basal and cauline or all cauline; alternate; petiolate or sessile; blades spatulate to oblanceolate or linear, margins usually entire (sometimes toothed or lobed on larger rosette leaves), faces densely to sparsely arachno-villous or ± strigillose, often gland-dotted as well. Heads radiate, usually in compact, corymbiform arrays or glomerulate clusters (borne singly in P. cooperi). Involucres cylindric to campanulate or obconic, 2–7 mm diam. Phyllaries persistent, 5–12 in 1–2 series (erect in fruit, distinct, oblong to lanceolate, bases ± indurate). Receptacles flat or convex, smooth or ± pitted (without setiform enations, sometimes gland-dotted), epaleate. Ray florets 1–8, pistillate, fertile; corollas yellow to orange (marcescent, spreading or reflexed in fruit). Disc florets 5–25+, bisexual, fertile; corollas yellow to orange, tubes shorter than narrowly cylindric throats, lobes 5, deltate (equal, papillate abaxially). Cypselae cylindric to clavate or obpyramidal, sometimes weakly obcompressed (ray), all striate-ribbed, usually glabrous, sometimes gland-dotted (villous in P. gnaphalodes, sometimes hirtellous in P. tagetina); pappi of 4–8 ± oblong or elliptic to lanceolate or lance-subulate, entire (lacerate in P. gnaphalodes) scales (without prominent midribs). x = 16.
Species 7 (6 in the flora): United States, Mexico.
My treatment of psilostrophes closely follows that by R. C. Brown (1978). Psilostrophe mexicana R. C. Brown is known from Chihuahua and Durango.
SELECTED REFERENCES
Brown, R. C. 1978. Biosystematics of Psilostrophe (Compositae: Helenieae). II. Artificial hybridization and systematic treatment. Madroño 25: 187–201. Turner, B. L., M. W. Turner, and J. C. Crutchfield. 1988. Populational analyses and new combinations in Psilostrophe tagetina and P. gnaphalodes (Asteraceae, Heliantheae). Phytologia 65: 231–240.
