Rock daisy [Greek peri, around, and tyle, a callus, alluding to calloused cypselae margins]

Sharon C. Yarborough, A. Michael Powell

Annuals, perennials, subshrubs, or shrubs, 2–45(–75) cm (glabrous or hairy, often gland-dotted). Stems erect to pendent. Leaves mostly cauline; often proximally opposite, distally alternate; petiolate or sessile; blades usually 3-lobed, ultimate margins entire, toothed, or lobed. Heads radiate or discoid, borne singly or in corymbiform arrays. Involucres campanulate, cylindric, funnelform, or hemispheric, 3–15 mm diam. Phyllaries persistent, 5–28 in (1–)2(–3) series (distinct, linear to ovate, equal or subequal, flat or keeled, glabrous or hairy, apices obtuse, acute, or attenuate). Receptacles flat or convex, pitted, epaleate. Ray florets 0, or (1–)3–18, pistillate, fertile; corollas cream, yellow, or white (showy or rudimentary). Disc florets 5–200, bisexual, fertile; corollas cream, yellow, or white, tubes shorter than or nearly equal to cylindric, funnelform, or campanulate throats, lobes 4, ± deltate (acute; stamens 4; style branches flattened, linear, usually tapering to fine, minutely hairy tips). Cypselae (black) flattened to subcylindric, linear to oblanceolate or obovate (margins ± calloused and glabrous, hairy, or ciliate, faces usually hairy, sometimes glabrous); pappi 0, or persistent or falling, of 1–35 bristles plus callous crowns or hyaline scales. x = 17, 19.

Species 66 (35 in the flora): United States, Mexico, South America.

Most species of Perityle are rock-dwelling subshrubs exhibiting geographic speciation; most are found in the eroded mountain and basin region of the southwestern United States.