It is an annual or perennial herb taking a multibranched erect form up to about 60 centimeters tall.

The oval green leaves are one or two centimeters long and are covered in tiny glands.

Where H. mutilum is native, it is variable in size and leaf shape but is still easily identified.

However, in Canada, characteristics that typically separate H. mutilum from Hypericum boreale break down such that they are treated as subspecies.

This variety was transferred to species rank by Bicknell while he simultaneously made a combination under H. mutilum.

The species grows sympatrically with H. mutilum and in Nova Scotia the two become very difficult to distinguish.

In these coastal populations, the terminal stem node is longer or absent as compared to the rest of the species, and thus the variety has been more recently promoted to a subspecies.

[5] Hypericum mutilum is a glabrous perennial or annual herb that is erect or decumbent, growing 15–60 cm (5.9–23.6 in) tall.

Leaves have three to five basal veins with somewhat prominent ascending branches, and lax, obscure tertiary reticulation.

The leaves are variable in shape but are most commonly broadly ovate or suborbicular, and have a pale underside.

The subspecies only occurs in scattered populations in low grounds and coastal mud from New Jersey to Florida and west to Texas.

The subspecies occurs from Newfoundland west to Manitoba, Wisconsin, and Minnesota and south to Virginia.

[4] Hypericum mutilum grows in ditches, marshes, shorelines, and occasionally in moist woods and fields.

[9] The plant is native to Eastern Canada and the United States, where it occurs in the north from south-eastern Manitoba to southern Ontario to Newfoundland, in the south to Florida, and in the west to Texas.

[10] It has been introduced to France in Landes, to Italy in Tuscany, to Poland in Silesia, to Mexico (where it may be partly native), to Honduras, Ecuador, Peru, Brazil, New Zealand, and Hawaii.

[4] Similar to some other species of Trigynobathys, H. mutilum grows in moist or muddy habitats where its seeds adhere to wading birds.