Large-flowered gaura is a tall annual or biennial with an erect stalk, branching near the top, and often hairy stems or leaves. Flowers on long, many-flowered spikes and are 4-parted. The 4 petals are all positioned in the upper half of the flower, opening at dusk, pointing upward and are white at first, turning pink later; they are curved back and about ⅝ inch long; the 8 stamens point forward and curve downward. The overall effect looks like a small butterfly. The stigma has 4 lobes. Blooms June–October. Stem leaves alternate, sessile, lance-shaped with widely spaced teeth, to 4 inches long. Small leaflets arise at the bases of larger leaves.
Similar species: Three other former members of the genus Gaura are known in Missouri: false gaura (O. glaucifolia, formerly G. linifolia), velvety gaura (O. curtiflora, formerly G. parviflora), and scarlet gaura (O. suffrutescens, formerly G. coccinea). Of these, velvety gaura is the most common, being scattered mostly in the western half of the state; its stems are densely haired, and compared to large-flowered gaura, its flowers are smaller and more actinomorphic (radially symetrical as opposed to bilaterally symmetrical).