327. Flaveria Jussieu, Gen. Pl. 186. 1789.
[Latin flavus, yellow]
Sharon C. Yarborough, A. Michael Powell
Annuals, perennials, or subshrubs, to 200+ cm [trees to 400 cm] (usually ± succulent, herbage usually glaucous). Stems (often purplish) erect or decumbent, branched distally or ± throughout. Leaves cauline; opposite (decussate); petiolate or sessile (weakly connate to connate-perfoliate); blades (often 3-nerved) oblong-ovate to lanceolate or linear, margins entire, serrate, or spinulose-serrate, faces glabrous or short-pubescent. Heads radiate or discoid, usually in tight or loose aggregations in (often flat-topped) ± corymbiform arrays or glomerules. Involucres oblong, urceolate, cylindric, or turbinate, 0.5–2 mm diam. Phyllaries persistent, 2–6(–9) in ± 1 series (linear, concave, or boat-shaped, subequal). Receptacles convex, epaleate ("receptacles" of glomerules sometimes setose). Ray florets 0–1(–2), pistillate, fertile; corollas yellow or whitish (laminae inconspicuous). Disc florets 1–15, bisexual, fertile; corollas yellow, tubes shorter than to about equaling funnelform to campanulate throats, lobes 5, ± deltate. Cypselae (black) weakly compressed, narrowly oblanceolate or linear-oblong (usually 10-nerved, glabrous); pappi usually 0, sometimes persistent, of 2–4 hyaline scales, or coroniform (of connate scales). x = 18.
Species 21 (8 in the flora): United States, Mexico, West Indies (Greater Antilles), Central America, South America, Asia (India), Africa, Australia.
Members of Flaveria are frequently found in alkaline, saline, and gypseous soils, often in disturbed and moist areas. Heads of Flaveria may be either radiate or discoid; when both are present in the same capitulescence, the discoid heads tend to be central and the radiate heads peripheral. Many species of Flaveria have persistent sheathing leaf bases that ring the stems after the leaves have fallen.
Flaveria is notable because certain species exhibit C3 photosynthesis, some C3–C4 (intermediate) photosynthesis, and others (F. brownii, F. bidentis, F. campestris, and F. trinervia in the United States) classic C4 photosynthesis.
SELECTED REFERENCE
Powell, A. M. 1978. Systematics of Flaveria (Flaveriinae–Asteraceae). Ann. Missouri Bot. Gard. 65: 590–636.
