''Triadenum'', known as marsh St. John's worts, is a small

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial n ...

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 ...

s in the family Hypericaceae. The genus is characterized by opposite, blunt-tipped leaves and pink flowers with 9

stamen The stamen (plural ''stamina'' or ''stamens'') is the pollen-producing reproductive organ of a flower. Collectively the stamens form the androecium., p. 10 Morphology and terminology A stamen typically consists of a stalk called the filame ...

s. They are distributed in North America and eastern Asia. Acceptance of this genus is varied. Kew's

Plants of the World Online Plants of the World Online (POWO) is an online database published by the Royal Botanic Gardens, Kew. It was launched in March 2017 with the ultimate aim being "to enable users to access information on all the world's known seed-bearing plants by ...

and the Database of Vascular Plants of Canada (VASCAN) treat it as a junior synonym of '' Hypericum'' and the ''

Flora of North America The ''Flora of North America North of Mexico'' (usually referred to as ''FNA'') is a multivolume work describing the native plants and naturalized plants of North America, including the United States, Canada, St. Pierre and Miquelon, and Greenla ...

'' and '' Flora of China'' treat it as separate. The situation arises from B. R. Ruhfel et al. (2011)'s genetic study describing ''Triadenum'' as subsumed under ''Hypericum'' and later genetic results disagreeing with this assessment. Under ''Hypericum'', the species are mostly treated as the section ''Hypericum'' sect. ''Elodea''.

Species

''Triadenum'' contains the following 6 species according to ''Flora of North America'' and ''Flora of China'': * ''

Triadenum breviflorum ''Triadenum'', known as marsh St. John's worts, is a small genus of flowering plants in the family Hypericaceae. The genus is characterized by opposite, blunt-tipped leaves and pink flowers with 9 stamens. They are distributed in North America an ...

'' (Wall.) * ''

Triadenum fraseri ''Triadenum fraseri'', commonly known as bog St. John's wort, Fraser's St. John's wort, and Fraser's marsh St. John's wort, is a perennial flowering plant in the family Hypericaceae that grows in wetlands of Canada and the northern United States. ...

'' * ''

Triadenum japonicum ''Triadenum'', known as marsh St. John's worts, is a small genus of flowering plants in the family Hypericaceae. The genus is characterized by opposite, blunt-tipped leaves and pink flowers with 9 stamens. They are distributed in North America an ...

'' (Thunb.) * ''

Triadenum tubulosum ''Hypericum tubulosum'', the lesser marsh St. Johnswort or southern marsh St. John's-wort, is a species of flowering plant in the family Hypericaceae. Formerly classified as synonym ''Triadenum tubulosum'', the species is found across the Souther ...

'' * '' Triadenum virginicum'' * ''

Triadenum walteri ''Hypericum walteri'', the greater marsh St. Johnswort or Walter's marsh St. John's Wort, is a flowering plant endemic to the eastern United States, from Texas to Delaware north to Illinois Illinois ( ) is a U.S. state, state in the Midw ...

References

Malpighiales genera Hypericaceae {{Triadenum-stub