Chrysogonum is a genus of low-growing perennial herbs in the family Asteraceae (order Asterales), native to eastern North America. The genus was erected by Carl Linnaeus in 1753 and is best known for the species Chrysogonum virginianum, commonly called green and gold. Taxonomic circumscription has varied: some treatments recognize a single species with multiple varieties, while others accept up to seven species including four Madagascan taxa (which may alternatively be placed in Aspilia).
Plants reach 2–50 cm in height, arising from fibrous-rooted rhizomes. Stems are erect to ascending when flowering, and prostrate vegetative stolons may also be produced. The opposite, petiolate leaves have elliptic-ovate to deltate-ovate blades with cordate to cuneate bases and crenate margins. Flower heads are radiate, borne singly or in pairs, with cupulate-hemispheric involucres 7–10 mm across. Each head contains 5–6 pistillate, fertile yellow ray florets and 25–50 functionally staminate yellow disc florets. The genus is morphologically distinctive for its “cypsela-complex”: each ray floret’s pistil is fused to an inner phyllary, three paleae, and their associated disc florets, forming a unit that disperses as a whole. These complexes bear an elaiosome — a fleshy, oil-rich structure that attracts ants, which carry them to their nests and disperse the seeds intact.
Chrysogonum virginianum is cultivated as an ornamental ground cover, valued for its bright yellow blooms and low habit.
Etymology
The name Chrysogonum derives from the Greek chrysos (gold) and gonos (seed), alluding to the bright yellow, hemispheric flower heads or to the fertile cypselae (seed-like fruits) produced from the distinctive cypsela-complexes of the ray florets.
Distribution
Chrysogonum is native to the eastern United States. Under the narrower circumscription followed by Flora of North America, the genus is confined to this region. A broader circumscription (adopted by Plants of the World Online as of 2024) extends the range to include Madagascar, though the Madagascan species may alternatively be classified in the genus Aspilia.
Ecology
Chrysogonum exhibits a specialized ant-dispersal mutualism. Each cypsela-complex includes an elaiosome — a fleshy, oil-bearing structure at the base of the phyllary. Ants carry the complexes into their underground nests, chew off the nutritious elaiosomes, and return the undamaged cypselae to the soil surface, effectively dispersing the seeds.
Cultivation
Chrysogonum virginianum, commonly known as green and gold, is cultivated as an ornamental ground cover for its bright yellow flowers and low, spreading habit. All three recognized taxa of the genus are used as garden plants and are sold in nurseries under horticultural names.
Taxonomy Notes
The taxonomy of Chrysogonum has been contentious. Carl Linnaeus established the genus in 1753 with the single North American species C. virginianum. In the 20th century, Jean-Henri Humbert added four Madagascan species (1958 onward), and some treatments recognize up to seven species. Stuessy (1977) reduced the genus to a single North American species with two varieties. Nesom (2001) recognized three allopatric varieties; in 2020 he elevated one variety to species rank as C. repens. The Madagascan species may alternatively be placed in Aspilia. As of 2024, both broader and narrower circumscriptions remain in active use.
