S. angularis grows 0.8–0.9 metres (2.5–3 ft) tall, although in the first year this biennial plant appears only as a low rosette of leaves.

The stems are 4-sided, appearing as a square in cross section, and glabrous, with flexible, thin wings on the edges.

[4][6] The plant blooms from June to September with fragrant pink (occasionally white) flowers that are up to 2.5 centimetres (1 in) across.

Yellowish triangular markings on the inner edge of the lobes give the appearance of a star in the middle of the flower.

[8] S. angularis is found in a variety of habitats, in glades, along roadsides, in fields, and along the margins of woods.