Hypericum harperi, the sharplobe St. Johnswort or Harper's St. John's wort, is a perennial flowering plant in the family Hypericaceae.

Webb, in his dissertation, referred to H. incertum as the cypress pond St. John's wort.

acutifolium (and previously identified as that variety), H. harperi remains distinct in its aquatic habitat and related aerenchymatous stem base.

[2] No other species of this H. denticulatum complex has the extensive rhizomes of H. harperi, a specialization indicative of its aquatic habitat and an adaptation shared with its coinhabitants Rhynchospora careyana, Oxypolis canbyi, and Lobelia boykinii.

The lanceolate leaves have a plane margin with an acute apex and a cuneate base.

The sepals are typically unequal, lanceolate, and have linear glands that become punctiform distally.

[2] Hypericum harperi grows in swamps as well as wet pine barrens, especially the shallows of depressional wetlands (Carolina bays).