Flower:

Elongating cluster of stalked flowers at the top of the stem. Flowers are tiny, less than 1/8 inch across, with 4 yellow petals notched at the tip. The green sepals behind the flower are sparsely hairy and more than half as long as the petals.

Leaves and stems:

Basal leaves may or may not be in a rosette around the base. Leaves are up to 1 inch long and ½ inch wide, becoming smaller as they ascend the stem, densely hairy, typically with a few irregular teeth around the edges. Basal leaves are oval to somewhat spatula-shaped and stalked, stem leaves are egg-shaped to oblong-elliptic and stalkless. Stems are densely hairy in the lower plant, smooth in the upper plant, unbranched or branching near the base.

Fruit:

Fruit is a flattened pod, oblong to elliptic, about 1/3 inch long. Fruits become widely spaced as the raceme lengthens, the flower stalk spreading and lengthening to an inch or more.

Notes:

There is conflicting information on whether Yellow Whitelow-grass is native or not. About half my references say yes, indicating it is a circumpolar species, the rest say it was introduced from Europe or Asia. The plant list published by the Minnesota DNR says it is native, so we're going with that—when the DNR changes its designation we'll go along with that, too. Yellow Whitlow-grass is not likely to be confused with another species when flowering, though its tiny flowers and sparse appearance may make it go unnoticed. When it first starts blooming in early spring, it is only a few inches tall with the flowers looking like tiny yellow dots in the grass—easily overlooked.