| Author | (L.) Rafinesque | |
| Distribution | A bimodal range in the state. Present over most of the Coastal Plain; however, no records for many northwestern counties. A few records for the southern Mountains, but no records for the Piedmont other than a recent one from Anson County, very close to the Coastal Plain.
This species has a rather odd range. It is widespread over eastern Canada and throughout New England and NY to PA, but southward is spottily distributed south to southern FL and eastern TX. There are relatively few records west to WI.
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| Abundance | In the southern and eastern portions of the Coastal Plain, it is uncommon to fairly common, at least locally. Very rare in most of the northwestern Coastal Plain; and also very rare in the southern Mountains. | |
| Habitat | This species grows in marshes, openings in swamps, and other very wet ground, often in peaty sites, and typically in blackwater habitats. In the mountains it occurs in bogs. As it is widespread in all Sandhills counties, this fact makes it clear that the species favors blackwater wetlands; the similar T. walteri – scarce in the Sandhills -- is the species that is “dominant” in the brownwater wetlands. | |
| Phenology | Flowers and fruits from July to September. | |
| Identification | This is an erect deciduous herb that grows to an average height of 1 foot tall. It is typically only sparsely branched, but it and other Triadenum species typically grow in colonies. It has opposite, elliptic to ovate leaves growing to about 2 inches long; the tips are quite rounded. Its distinguishing character is the strongly clasping leaf bases; each leaf “joins” the opposing leaf such that the stem appears to grow through each pair of leaves. It has five pink-petaled flowers in clusters at the branch tips. The similar and more common and widespread T. walteri has leaves with a distinct petiole and which are rounded or tapered at the base. The rare T. tubulosum has leaves that are rounded or tapered at the base, as well, but they have no petioles showing. | |
| Taxonomic Comments | This species and the more northerly T. fraseri are often merged into a single species, generally named as T. virginicum. Weakley (2020) transferred the pink-flowered Hypericum species to Triadenum.
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| Other Common Name(s) | Common Marsh St. John’s-wort | |
| State Rank | S3S4 | |
| Global Rank | G5 | |
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| US Status | | |
| USACE-agcp | | |
| USACE-emp | | |
