Northern Prairie Wildlife Research Center
Southern Wetland Flora
Field Office Guide to Plant Species
Marsh St. Johnswort
Triadenum virginicum (L.) Raf.
- Family: St. Johnswort (Hypericaceae)
- Flowering: August-September
- Field Marks: The genus Triadenum is characterized by opposite, blunt-tipped leaves and pink
flowers with 9 stamens.
- Habitat: Bogs, swamps, marshy shores, wet woodlands, sometimes growing on floating mat of
vegetation and on stumps and floating logs in swamps.
- Habit: Perennial herb with slender rhizomes.
- Stems: Upright, usually unbranched, smooth, up to 28 inches tall.
- Leaves: Opposite, simple, ovate to
oblong, broadly rounded at the tip, rounded or even cordate-clasping at the base, smooth, toothless,
black-dotted, up to 3 inches long, up to 1 inch broad.
- Flowers: Crowded in terminal and axillary clusters,
pink, up to 2/3 inch across.
- Sepals: 5, green, free from each other, up to 1/3 inch long.
- Petals: 5, pink,
free from each other, up to 1/2 inch long.
- Stamens: 9.
- Pistils: Ovary superior; styles 3, separate from
- Fruits: Capsules ovoid, up to 1/2 inch long, with dark brown seeds.
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