Heterotheca is a genus of roughly 70 annual and perennial herbs in the family Asteraceae (order Asterales), native to North America and colloquially known as goldenasters, camphorweed, and telegraph weed. Plants bear daisy-like flower heads with yellow disc florets and, in most species, yellow ray florets, and they occupy a wide range of habitats from mesic meadows to xeric scrubland and desert margins across the United States, Canada, Mexico, and as far south as Belize.
The genus is distinguished by a characteristic of its cypselae (single-seeded fruits): in several species the achenes produced by the disc florets differ markedly in shape from those produced by the ray florets — a trait commemorated in the name itself, drawn from the Ancient Greek for "different chest" or "different ovary." Several species now placed in Heterotheca were formerly classified in the related genus Chrysopsis.
Notable members include H. inuloides (Mexican arnica), used medicinally in Mexico; H. subaxillaris (camphorweed), one of the most widespread species ranging from Belize to the northeastern United States; H. grandiflora (telegraph weed), a familiar annual of disturbed roadsides in California; and H. monarchensis (monarch golden aster), a narrow endemic of Fresno County, California. The foliage of several species, particularly H. subaxillaris, serves as a larval food plant for moths in the genus Schinia (S. lynx, S. nubila, and S. saturata).
Etymology
The name Heterotheca derives from the Ancient Greek ἕτερος (héteros, "other, different") and θήκη (thḗkē, "case" or "ovary"), and alludes to the difference in shape between the cypselae produced by the disc florets and those produced by the ray florets in certain species of the genus.
Distribution
Heterotheca is native to North America, distributed from western and central Canada south through the contiguous United States and into Mexico (including Nuevo León, Coahuila, Oaxaca, Durango, and Baja California), with H. subaxillaris extending as far south as Belize. Species are found in habitats ranging from mesic grasslands and open woodlands to xeric desert margins, rocky slopes, and disturbed roadsides.
Ecology
Most Heterotheca species occupy mesic to xeric open habitats — prairies, desert scrub, rocky slopes, and roadsides — across temperate North America. Several species, particularly H. subaxillaris, provide larval host plants for noctuid moths in the genus Schinia (S. lynx, S. nubila, S. saturata), linking the genus to pollinator and insect food-web networks of North American grasslands and shrublands.
Taxonomy Notes
Several species now recognized in Heterotheca were formerly placed in the closely related genus Chrysopsis, and the boundaries between these genera have been revised multiple times. The genus belongs to the tribe Astereae within Asteraceae.
