Hypericum tubulosum, the lesser marsh St. Johnswort or southern marsh St. John's-wort, is a species of flowering plant in the family Hypericaceae.

[2][3] Formerly classified as synonym Triadenum tubulosum,[1] the species is found across the Southern United States and Midwest.

[2][4] Lesser marsh St. Johnswort is a perennial herb that grows to approximately 32 inches (81 cm) tall.

Its pink flowers bloom in August and September.

[4] The seeds of H. tubulosum closely resemble those of the extinct paleospecies Hypericum tertiaerum.