''Silphium trifoliatum'', commonly known as whorled rosinweed, is a

species In biology, a species is the basic unit of Taxonomy (biology), classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of ...

flowering plant Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (), commonly called angiosperms. They include all forbs (flowering plants without a woody stem), grasses and grass-like plants, a vast majority of ...

in the family

Asteraceae The family Asteraceae, alternatively Compositae, consists of over 32,000 known species of flowering plants in over 1,900 genera within the order Asterales. Commonly referred to as the aster, daisy, composite, or sunflower family, Compositae ...

. It is native to the eastern

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., federal district, five ma ...

, where it is found east of the

Mississippi River The Mississippi River is the second-longest river and chief river of the second-largest drainage system in North America, second only to the Hudson Bay drainage system. From its traditional source of Lake Itasca in northern Minnesota, it ...

. Its natural habitat is open, grassy areas such as prairies, river cobble bars, and roadsides. It is a tall perennial that produces heads of yellow flowers in mid-summer through fall.''Silphium asteriscus'' var. ''trifoliatum''
Flora of North America This species is considered to be a variety of ''

Silphium asteriscus ''Silphium asteriscus'', commonly called starry rosinweed, is an herbaceous plant in the family Asteraceae. It is native to the eastern United States, from Oklahoma and Texas east to Florida and Pennsylvania Pennsylvania (; (Pennsylvani ...

'' by some authors. It can be distinguished by its smooth stems and leaves that are often in whorls of three. In contrast, ''S. asteriscus'' has scabrous to hispid stems and leaves, which are opposite or alternate. In addition, ''S. trifoliatum'' has eglandular pales (the bracts in the flower heads), while the pales of ''S. asteriscus'' are often glandular. There remains much disagreement about the best taxonomic treatment of the ''S. asteriscus'' complex.

References

{{Taxonbar, from=Q21877452 trifoliatum