[2] Its remaining habitat is considered seriously threatened and the plant is a federally listed endangered species in the United States.

[2][3] Thelypodium stenopetalum is a biennial herb producing decumbent stems up to about 80 centimeters long.

The basal leaves have thick, oblong to lance-shaped blades up to 15 centimeters long with smooth or rippled edges.

[4] Thelypodium stenopetalum can sometimes be found growing near pebble plain habitat, which contains several other rare plant species.

[4] This mustard is a food plant for the larva of the rare endemic Andrew's marble butterfly (Euchloe hyantis andrewsi).