Calochortus monophyllus is a species of flowering plant in the lily family known by the common name yellow star-tulip. It is native to the foothills of the Sierra Nevada and southernmost Cascades in California, its range probably extending north just into Oregon. It is a perennial herb producing a slender, sometimes branched stem up to about 20 centimeters tall. The basal leaf is 10 to 30 centimeters in length and does not wither at flowering. There may be smaller leaves located along the stem. The flower cluster bears 1 to 6 erect, bell-shaped flowers. Each flower has three pointed sepals and three more rounded petals, all bright to deep yellow. The petals may have some dark reddish spotting at the bases and are coated densely with yellow hairs on the inner surfaces. The fruit is a winged capsule one or two centimeters long.