Triadenum, known as marsh St. John's worts,[2] is a small genus of flowering plants in the familyHypericaceae. The genus is characterized by opposite, blunt-tipped leaves and pink flowers with 9 stamens. They are distributed in North America and eastern Asia.
Acceptance of this genus is varied. Kew's Plants of the World Online[3] and the Database of Vascular Plants of Canada (VASCAN)[4] treat it as a junior synonym of Hypericum and the Flora of North America[1] and Flora of China[5] 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.[6] Under Hypericum, the species are mostly treated as the section Hypericum sect. Elodea.[7]
Species
Triadenum contains the following 6 species according to Flora of North America and Flora of China:[1][5]
^Robson, Norman K.B. (11 April 2016). "And then came molecular phylogenetics—Reactions to a monographic study of Hypericum (Hypericaceae)". Phytotaxa. 255 (3): 181. doi:10.11646/phytotaxa.255.3.1.
