Niu Xi

Achyranthes bidentata (Niu Xi, two-toothed amaranth, ox-knee) is a perennial herb in the Amaranthaceae family, growing 70 to 120 centimeters tall, with quadrangular, conspicuously swollen, knee-like nodes (giving rise to both the Chinese common name Niu Xi, ox-knee, and English ox-knee). Stems are erect, sparsely branched, and finely pubescent. Leaves are opposite, elliptic to elliptic-lanceolate, 4 to 12 centimeters long, with entire margins, acuminate tips, and short petioles. The inflorescence is a slender terminal spike 3 to 5 centimeters long that elongates in fruit to 10 to 15 centimeters, bearing numerous small greenish flowers that reflex downward against the rachis as they mature; each flower is subtended by a persistent bract and two stiff bracteoles tipped with sharp barbed spines that cling to clothing and animal fur, aiding dispersal. The medicinal root is long, cylindrical, slightly twisted, 30 to 90 centimeters long and 0.4 to 1 centimeter thick, externally grayish-yellow, internally pale yellowish-brown. Native to East Asia, India, and adjacent regions.