Pteroxygonum giraldii (红药子 hong yao zi) is a plant species in the genus Pteroxygonum, endemic at altitudes of 600-2000 meters in China's provinces of Gansu, Hebei, Henan, Hubei, Shaanxi, Shanxi, and Sichuan. It grows to more than 3 meters in height, with leaf blades triangular or triangular-ovate in shape, 4-7 × 3-6 cm. Annulatin is an O-methylated flavonol found in the roots of P. giraldii.