Information:

Purple duckweed, duckweed family purple bamboo plum genus, perennial lance herb, 20 to 50 cm high. Stem multi-branched, fleshy, purplish red, lower creeping, often bearing fibrous roots at the nodes, upper nearly erect. Leaves alternate, oblong, 6 to 13 centimeters long, 6 to 10 millimeters wide, apex acuminate, entire, base clasping the stem and forming a sheath, the mouth of the sheath with long white lashes, dark green above, greenish-purple on the margin, purple-red below. Flowers densely borne on bifurcate inflorescence stalks, below linear-lanceolate bracts, ca. 7 cm; sepals 3, green, ovoid, persistent; petals 3, blue-purple, broadly ovate; stamens 6, 2 merchantable, 3 staminodes, another with short, slender filaments and no anthers; pistil 1, ovary ovate, 3-loculed, style filiform and long, stigma capitate. Capsule ellipsoid, with 3 elevated ribs. Seeds trigonous semiorbicular, han brown. Flowering in summer and fall. Purple Duckweed is also known as purple brocade grass and purple bamboo plum, and is widely cultivated. The whole plant is purplish red all year round, and the branches are either trailing or drooping, which is distinctive and of high ornamental value. Below are pictures of purple duckweed.

Conclusion:

The information indicates that the plant you are asking about is the Purple Duckweed, genus Purple Duckweed, family Duckweed.