Flower:

Elongating racemes at the top of the plant. Flowers are tiny with 4 spreading, pale yellow petals rounded or notched at the tip. In the center are 6 yellow stamens and a stout green style. The 4 sepals surrounding the base of the flower are oblong to egg-shaped and green. Flower stalks are spreading to ascending, less than ~¼ inch (2 to 4 mm) long; stalks and sepals are covered in star-shaped hairs. The racemes elongate as the plant matures, with a tight round cluster of open flowers at the tip, spent flowers fading to white, and fruit forming below.

Leaves and stems:

Leaves are alternate, up to ~1 inch (.5 to 3 cm) long, less than ¼ inch (.5 to 4 mm) wide, mostly broadest above the middle, blunt to pointed at the tip, tapering at the base, short-stalked to stalkless. Edges are toothless, surfaces are covered in star-shaped hairs with 8 to 20 rays. Stems are single or multiple from the base, erect, ascending, or prostrate from the base and rising near the tip (decumbent), branched or not, and densely covered in star-shaped hairs.

Fruit:

The sepals wither away as fruit develops. Fruit is a 2-chambered capsule less than ¼ inch (2.5 to 4 mm) long, round in outline, flattened around the edges and bulging in the center as seed develops, the remains of the persistent style at the tip, and smooth across the surface. Inside the capsule are 4 oval seeds.

Notes:

Desert Madwort is an occasional weed found on roadsides, agricultural fields, gravel pits, parking lots and other areas with disturbed soils, and, like many weeds, is no doubt under-reported in the state. It is very similar to the related Pale Madwort (Alyssum alyssoides), which is much like it in all respects except its capsules are covered in star-shaped hairs and sepals are persistent. We've encountered both species at various campgrounds in Minnesota, where weed seed is often transported on car tires.