Flower:

Elongating cluster of stalked flowers at the ends of branching stems, with a few to several flowers open at the tip and fruit developing below. Flowers are about 1/8 inch across with 4 rounded white petals and 6 yellow stamens. The sepals behind the flower are about half as long as the petals and have a few hairs around the edges.

Leaves and stems:

Leaves are primarily basal with a few leaves widely spaced on the stems. Basal leaves are 1 to 2 inches long, up to ½ inch wide, oblong to narrowly spatula shaped, with rounded tips, stiff hairs across the surface, toothless or with tiny teeth around the edges, narrowing at the base to a stalk. Basal leaves may wither away as the plant matures.

Stem leaves are about 1 inch long, up to 3/8 inch wide, tapering to a point at both ends, stalkless and mostly toothless. Stems are bristly hairy at the base and hairless in the upper plant. Multiple stems may arise from the base.

Fruit:

Fruit is a slender cylindrical pod up to ¾ inch long, spreading or angled up, sometimes curved up.

Notes:

An interesting weed, chosen for plant study and experiments worldwide, even on the International Space Station, due to its extremely short life cycle and ease of propagation. It can go from seed to maturity in about 6 weeks, and easily colonizes when left to its own devices. It is similar in appearance to the native Lyre-leaved Rock Cress (Arabidopsis lyrata), which has larger flowers, lobed or divided basal leaves, narrower stem leaves, and does not form colonies. Mouse-ear Cress is no doubt under-reported in Minnesota.