Vascular Plants of North Carolina
Account for Southern Marsh St. John's-wort - Triadenum tubulosum   (Walter) Gleason
Members of Hypericaceae:
Members of Triadenum with account distribution info or public map:
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Section 6 » Order Theales » Family Hypericaceae
Author(Walter) Gleason
DistributionPoorly known owing to difficulty in identification. Apparently widely scattered in the Piedmont, but a few records for the northern Coastal Plain and one from the northern Mountains. Somewhat disconcerting is that most or all records outside the Piedmont do not seem to be supported by specimens. Further distribution inventory is needed.

Primarily found in the Southeastern states, ranging north to MD and MO, and south to western FL and eastern TX. However, records are scattered in most states, maybe due to being overlooked.
AbundanceApparently very rare to rare. The NCNHP has recently moved the species from its Watch List to now Significantly Rare.
HabitatThis is a species of shallow water or mud, in non-flowing waters, such as pond and lake margins, old river oxbows, wooded pools, etc. Weakley (2018) suggests that drawdown zones of lakes and river sloughs are important habitats.
PhenologyBlooms in August and September, and fruits shortly thereafter.
IdentificationThis is a fairly widely branching herbaceous Triadenum, growing to about 2 feet tall. It has opposite, elliptic to oblong leaves that average 2 inches long, and which are rounded at the tip but are tapered/cuneate to the base; there is no petiole. An important identification character is its sessile leaves that are not clasping; T. virginicum is very similar but the leaves clasp the stem with its cordate bases. T. walteri is also similar but it has leaves that taper toward the stem but have short petioles that average 1/4-inch long. All three have pink, 5-petaled flowers. There are several other characters that separate these three, such as sepal length and shape; see detailed keys for differences.
Taxonomic CommentsWeakley (2020) changed his position and the pink-petaled Hypericum species revert to Triadenum.

Other Common Name(s)Lesser Marsh St. John’s-wort
State RankS2
Global RankG4?
State StatusSR-O
US Status
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