During fall and winter, visitors are greeted at the MEMBG north entrance by a very showy Mexican sunflower, Tithonia diversifolia (Hemsl.) A. Gray, a proud member of the sunflower family, Asteraceae. Tithonia was named for Tithonus, a legendary Trojan loved by the dawn goddess Eos, who irreligiously turned him into a grasshopper. The genus occurs throughout Middle America and the West Indies and has become naturalized around the tropics.
For us, Tithonia diversifolia is a rangy shrub with wide and pithy, unbranched ascending stems four to six meters tall, mostly leafless in the lower zone. Leaf arrangement is helically alternate. The typical leaf is fifteen to thirty centimeters long and has a minute roughness (scabridity) on the upper surface. The whitish petiole (acuminate) is fringed halfway with blade tissue, at the terminus of which three whitish midveins vascularize a mitten-like blade with three or five prominent lobes. Occasionally, new shoots possess unlobed leaves.
Our interest in this species focuses primarily on the sunflower head, which is not a single fifteen-centimeter flower but rather an orange-yellow inflorescence composed of many small flowers crowded together. Around the perimeter, eleven to thirteen ray florets (ligulate flowers) frame 200 to 300 tubular disk florets, which smell like a daisy. After pollination, the inferior ovary of each disk floret develops as a hairy, gray, flattened, dry, one-seeded fruit (an achene) hidden by papery, brown-tipped bracts that, at maturity, are arranged into a hemispherical mound. These and other characteristics indicate that Tithonia belongs to the same tribe (Heliantheae) and subtribe (Helianthinae) of genera as the common sunflower (Helianthus annuus) and Wedelia trilobata, which is used widely around MEMBG as a ground cover.