4. Triadenum walteri (J. F. Gmelin) Gleason, Phytologia. 2: 289. 1947.
Hypericum walteri J. F. Gmelin, Syst. Nat. 2: 1159. 1792 (as Hypericon); Elodes floribunda Spach; E. petiolata Pursh; Gardenia petiolata (Pursh) Farwell; Hypericum paludosum Choisy; H. tubulosum var. walteri (J. F. Gmelin) Lott; Triadenum petiolatum (Pursh) Britton
Herbs erect, to 10 dm, sometimes with ascending branches in distal 1/2+. Stems: internodes 4-lined at first, then terete. Leaves petiolate, petiole 2–15 mm; blade narrowly elliptic to narrowly oblong, 30–150 × 10–35 mm, base cuneate, apex rounded, gland dots laminar and intramarginal. Inflorescences interrupted spiciform-cylindric, 3-flowered from terminal node, sometimes with subsessile flowers or pedunculate triads and/or flowering branches from to 8 proximal nodes. Flowers 7–10 mm diam.; sepals narrowly oblong to narrowly elliptic or lanceolate, 3–5 × 1–1.5 mm, apex obtuse to rounded; petals narrowly obovate, 5–7 mm; stamen fascicles 3–5 mm; filaments 1/2+ connate; styles 0.8–1.2 mm. Capsules cylindric, 7–12 × 3–4 mm, apex subacute. Seeds 0.8–1.1 mm.
Flowering late summer (Jul–Sep). Swampy or marshy ground in woods, pond or lake margins, on fallen logs; 0–400 m; Ala., Ark., Del., Fla., Ga., Ill., Ind., Ky., La., Md., Miss., Mo., N.J., N.C., Ohio, Okla., S.C., Tenn., Tex., Va., W.Va.
The petiolate leaves usually distinguish Triadenum walteri from the other three North American species of Triadenum (see note under T. tubulosum.