Hist. Acad. Roy. Sci. Mém. Math. Phys. (Paris, 4to) 1750: 377. 1754.
Annuals, perennials, subshrubs, or shrubs, 10–120[–200+] cm. Stems erect, usually strictly branched. Leaves cauline; opposite or alternate; petiolate or sessile; blades orbiculate to linear or filiform, margins crenate or entire, faces usually glabrous (oil-glands scattered and/or at margins). Heads discoid, borne singly or in loose, ± corymbiform arrays. Calyculi 0. Involucres cylindric to campanulate [turbinate], 3–12 mm diam. Phyllaries 5–10 in ± 2 series (distinct to bases, oblong or lanceolate to linear, bearing oval to linear oil-glands). Receptacles convex to conic, pitted, epaleate. Ray florets 0. Disc florets (5–)10–80[–100+], bisexual, fertile; corollas usually yellow, sometimes whitish to greenish or purplish [brownish], tubes either very slender, much longer than funnelform throats, or stout, much shorter than narrowly cylindric throats, lobes 5, deltate to lanceolate (often unequal). Cypselae cylindric to fusiform, hirtellous to villous [glabrous]; pappi persistent, of 25–50(–100) coarse to fine bristles in 1–2+ series. x = 12.
sw United States, Mexico, West Indies (Antilles), Central America, South America.
Species ca. 25 (5 in the flora).
|1||Annuals; leaf blades oval or elliptic to obovate, 8–25+ mm wide||Porophyllum ruderale|
|1||Perennials, or subshrubs or shrubs; leaf blades linear to filiform, 1–5 mm wide||> 2|
|2||Corollas whitish or purplish||Porophyllum gracile|
|2||Corollas yellow (sometimes tinged reddish)||> 3|
|3||Subshrubs or shrubs, 20–60+ cm; phyllaries 7–10||Porophyllum scoparium|
|3||Perennials (rarely woody at bases), mostly 5–30 cm; phyllaries 5(–8)||> 4|
|4||Internodes mostly 1–5(–12) mm; leaf blades 8–15 × 2 mm; pappi: longer bristles 6–7 mm||Porophyllum pygmaeum|
|4||Internodes mostly 10–20+ mm; leaf blades 20–60 × 1–2 mm; pappi: longer bristles 8–10 mm||Porophyllum greggii|