Like all but one of the ten species of this genus in the US, sisymbrium loeselii
is a non-native plant, found in scattered parts of the majority of the western states, most commonly in the northern Rocky Mountains.
Stems grow vertically upwards, branching towards the top. The lower portion of the stem usually has a covering of bristly, backwards-pointing hairs; upper stems are hairless. Leaves grow in a rosette at the base, and along the stems, on stalks up to 2 inches in length. The leaves are quite distinctive, being divided into a large, triangular terminal lobe and one or two pairs of smaller side lobes, at the base. The terminal lobe is lined by large teeth. Leaf margins are sparsely bristly. Stem leaves are much smaller then those at the base.
The inflorescence is a dense cluster of small flowers, each formed of four oblong, greenish yellow sepals and four clawed, spatulate yellow petals, about twice as long - up to 0.3 inches. At the center are six stamens, with green filaments and yellow anthers. Fruits are slender cylinders up to 1.5 inches long, straight or curved.