Clustered Yellowtops

Flaveria trinervia is widespread and weedy; it often occurs in saline, gypseous, disturbed areas near permanent or ephemeral water sources in southern Florida and from Texas to southern California. It occurs also in scattered locations in some eastern states and has been reported from Alabama.

The heads of Flaveria trinervia, which usually contain just one floret, are either radiate or discoid; radiate heads tend to occur on the periphery of setose glomerules. Reduction of some of the floral features, including number of florets [0–1(–2)], phyllaries per head (2), and size of ray laminae, suggest that F. trinervia may be the most derived species in the genus.

Annuals, to 200+ cm (delicate or robust, glabrate or glabrous). Stems erect. Leaves petiolate (proximal, petioles 10–20 mm) or sessile (distal); blades lanceolate or oblanceolate to elliptic or subovate, 30–150 × (7–)10–40 mm, bases (distal) connate, margins serrate, serrate-dentate, or spinulose-serrate. Heads 30–300+, in tight, axillary, sessile glomerules (receptacles of glomerules setose). Calyculi 0. Involucres oblong and cylindric or angular, 3.8–4.5 mm. Phyllaries usually 2, oblong (closely investing and falling with mature cypselae). Ray florets 0–1; laminae pale yellow or whitish, oblique or suborbiculate, 0.5–1 mm. Disc florets 0–1(–2); corolla tubes 0.5–1.4 mm, throats campanulate, 0.5–0.8 mm. Cypselae oblanceoloid to subclavate, 2–2.6 mm (rays longer); pappi 0. 2n = 36.

Odera trinervia Sprengel, Bot. Gart. Halle, 63. 1800

trinervia: 3-veined

Much-branched erect or procumbent annual herb, usually up to 75 cm tall, rarely taller. Branches opposite, often pinkish-red, mostly hairless. Leaves opposite, yellowish-green, narrowly elliptic to oblanceolate, 1-7.5 cm long, 3-veined from the base, narrowing at the base into a pseudo-petiole; margin more or less finely toothed. Capitula numerous in congested axillary and terminal heads, yellow with very short ray-florets, 0.5-1 mm long.

Native to tropical America. Now a pantropical weed.

Flaveria trinervia (Spreng.) C. Mohr, Contr. U. S. Nat. Herb
6: 810. 1901.
Oedera trinervia Spreng. Bot. Gart. Halle 63. 1800. Brotera Conlrayerba Spreng. Jour. Bot. Schrad. 1800'-': pi. 5.
1807. Nauenbergia trinervata Willd. Sp. PI. 3: 2393. 1804.
1801. Not Flaveria Conlrayerba Pers. Brolcra trinervata Pers. Syn. PI. 2: 498. 1807. Flaveria repanda Lag. Gen. & Sp. Nov. 33. 1816. Brotera Sprengelii Cass. Diet. Sci. Nat. 34: 306. 1825. Flaveria trinervata Baillon, Hist. PI. 8: 55. L882.
A dichotomously and divaricately branched annual; stem erect, 3-12 dm. high, sometimes tinged with red, glabrate; leaves connate, lanceolate, 3-nerved, serrate, 3-9 cm. long, the lower short-petioled; cymes congested and head-like, 2 2.5 cm. broad, axillary, subtended by three pairs of leaves; heads small, usually 1 -flowered, the flower either subligulate and pistillate or regular and hermaphrodite; involucral bracts concave, 1 or 2, if the latter, the outer shorter; corolla of the pistillate flowers 1.5 mm. long, the ligule oblique, 3-dentate; corolla of the hermaphrodite flowers 2 mm. long; tube villous; throat campanulate; achene 2 mm. long, somewhat clavate; pappus wanting.
Type locality: Botanical garden, Halle (cultivated).
Distribution: Alabama to Arizona, Oaxaca, and Yucatan; Cuba; also in South America. Introduced at Westford, Massachusetts.

Flaveria australasica is an Australian plant species of yellowtops within the family Asteraceae. It has been found in New South Wales, Queensland, South Australia, Western Australia, and Northern Territory.

Flaveria australasica is very similar and possibly closely related to F. trinervia. Some authors treat the two as distinct species while others consider F. australasica as a synonym of F. trinervia.