Peritoma lutea is an easily recognizable species, producing elongated clusters of yellow flowers at the top of the upright, hairless, green stems, which may branch a few times towards the top. Flowers consist of four short, yellowish, lanceolate sepals and four longer, oblong petals around a group of stamens, which project outwards by nearly an inch. The filaments are topped by coiled anthers. Sepals have tiny teeth along their edges.
The palmate leaves grow at quite wide intervals all along the stem. Flowers form at the tip of the stem, which continues to grow, leaving withered blooms lower down; these develop into thin, green seed pods up to 1.5 inches long, so it is common to see both flowers and seeds on a single plant.