Harvard Pap. Bot. 11: 275. 2007.
Perennials; glabrous throughout. Rhizomes slender, 0.5–1 mm diam. Stems erect to ascending, branched, 1.5–2 dm. Rhizomal and basal leaves absent. Cauline leaves 3 or 4, 3- or 5-foliolate, petiolate, leaflets petiolulate; petiole 0.5–1.7 cm, base not auriculate; lateral leaflet blade linear to linear-lanceolate, 0.9–1.5 cm × 1–3 mm, margins entire; terminal leaflet (petiolule 0.3–0.5 cm), blade obovate to lanceolate (linear distally), 1.3–2.3 cm × 2–8 mm, base cuneate, margins entire or subapically 1- or 2-toothed. Racemes ebracteate. Fruiting pedicels ascending to suberect, 5–14 mm. Flowers: sepals oblong, 1.2–1.5 × 0.6–0.8 mm, lateral pair not saccate basally; petals white, oblanceolate, 2–2.5 × 0.8–1 mm, (not clawed, apex rounded); filaments: median pairs 1.5–1.8 mm, lateral pair 1–1.2 mm; anthers ovate, 0.2–0.3 mm. Fruits linear, 1–2 cm × ca. 1 mm; ovules 16–24 per ovary; style 0.5–0.7 mm. Seeds brown, oblong, 1.2–1.5 × 0.8–1 mm.
Phenology: Flowering Jul–Aug.
Habitat: Boggy slopes
Cardamine holmgrenii is known only from the type collection, from the Blue Mountains in Baker County.