Tithonia diversifolia (Hemsl.) A. Gray

• Title

  Tithonia diversifolia (Hemsl.) A. Gray

• Authors

  Nathaniel Lord Britton, Frances W. Horne

• Scientific Name

  Tithonia diversifolia (Hemsl.) A.Gray

• Description

  Flora Borinqueña Tithonia diversifolia Girasole Tithonia Family Carduaceae Thistle Family Mirasolia diversifolia Hemsley, Biologia Centrali Americana, Botany 2: 168. 1881. Tithonia diversifolia Asa Gray, Proceedings of the American Academy of Arts and Sciences 19: 5. 1883. Conspicuous, when in bloom, by large flower-heads with long, bright yellow ray-flowers, and often planted for ornament, this large Mexican and Central American herbaceous plant has occasionally established itself along roads in Porto Rico, apparently spontaneous from seed. It was introduced into the East Indies some years ago, and is recorded as having become a pest in Burma; as yet we have no evidence that it will become troublesome here. It has been established in Jamaica. Tithonia, named for Tithon, consort of Aurora, by the French botanist Desfontaines, first described in 1791, consists of six, or more species of tall herbs, natives of Mexico and Central America. They have large, stalked, alternate leaves, and large, terminal, stalked heads of discoid and radiate, yellow or orange flowers, with a nearly hemispheric involucre composed of broad, appressed bracts in 2 series, the receptacle bearing scales which envelope the disk-flowers. The ray-flowers are long and showy; the disk-flowers are nearly cylindric. The oblong achenes are compressed, or 4-sided; the pappus is composed of scales and bristles. Tithonia diversifolia (diverse leaves) is somewhat woody, branched, from 2 to 4 meters high, or sometimes vine-like and about 6 meters long, the young branches rather densely hairy. The finely hairy leaves, from 7 to 20 centimeters long, are mostly 3-lobed, or 5-lobed, with pointed lobes, and a narrowed base. The stalks of the flower-heads are from 5 to 25 centimeters long; the involucre is about 2 centimeters long, its bracts mostly blunt; the yellow, 3-toothed ray-flowers are 5 or 6 centimeters long. The hairy achenes are about 5 millimeters long. Tithonia rotundifolia, a related species, is also established in Porto Rico.