Annuals, 70-200 cm. Leaves: petioles 0-3.3 cm; blades deltate, 7-28 × 5.5-21.5 cm, abaxial faces sparsely hirsute (hairs larger on veins). Peduncles 17-36 cm. Phyllaries 13-16 in 3 series, linear to spatulate; outer 8-15 × 2.5-4.5 mm, apices acute, abaxial faces puberulent; inner 12-15.5 × 3.5-7 mm, apices acute, abaxial faces glabrous. Paleae 11-16.5 × 2-4 mm, mucros 3 mm. Ray florets 7-10; corollas yellow, laminae oblong, 9-15 × 4-6 mm. Disc florets 40-60. Cypselae 6-9 mm. 2n = 34.

Flowering Aug-Sep. Disturbed areas, canyons, watercourses; 900-1000 m; Ariz.; Mexico (Sonora).

Duration: Annual

Nativity: Native

Lifeform: Forb/Herb

General: Slender, moderately branched annual 0.5-2 m tall with whitish, striate stems sparsely to densely hispid-pilose with spreading; tuberculate-based, coarse hairs interspersed with finer ones, eventually glabrate.

Leaves: Lower leaves opposite, upper ones alternate, blades ovate to broadly triangular-ovate, acute to acuminate, 3-27 cm wide, 5-28 cm long, cuneately decurrent along petiole from a cuneate to broadly cordate base, crenate-dentate with mucronulate teeth, deep green and hispidulous with incurved hairs above, paler green and sparsely granular or hispidulous and hispid-pilose along veins beneath, petioles 2-10 cm long.

Flowers: Fistulose peduncles, striate, 10-30 cm long, spreadingly hispid-pilose and finely hispidulous; heads 2.5-3.5 cm wide, involucres of graduated bracts in 3 series, 1-2 cm tall, outer bracts lanceolate, oblong-ovate, acute to acuminate; rays 5-10, orange-yellow, oval-oblong 4-6 mm wide, 7-12 mm long; disk corollas 6-6.2 mm long, hispidulous on lobes, glandular-pilosulous below, tube about 1 mm long, throat cylindrical.

Fruits: Oblong-obovate cypselae, 8.5-9 mm long, pappus awn solitary on outer angle of cypselae, linear-subulate, 5-5.8 mm long.

Ecology: Found in rich soil along banks of streams, ditches, and margins of water bodies from 3,000-4,500 ft (914-1372 m); flowers August-September.

Notes: This plant is distinguishable by its orange rays and sunflower-like leaves and habit.

Ethnobotany: Unknown

Etymology: Tithonia comes from the Latin Tithon, who was the husband of Aurora, while thurberi is named for Dr. George Thurber (1821-1890).

Synonyms: None

Editor: SBuckley, 2010