Formerly listed as Polygonum, the two plants described offer showy flowers. Both merit vigilance, as they spread by rhizomes and can be highly invasive and difficult to eradicate. Don't plant them in unmanaged areas.
F. baldschuanica (Polygonum aubertii). SILVER LACE VINE. This extremely vigorous vine from Asia can cover a large space in a short time. It typically puts on 1015 ft. of new growth in a single season and can fully drape an arbor, fence, or gazebo in short order. Glossy, dark green leaves are arrowhead shaped, 1122 in. long. A frothy mass of fragrant, creamy white flowers, sometimes tinged with pink, smothers the plant in summer and fall. Prune silver lace vine severely to keep it in bounds; you can cut it to the ground in winter and it will resprout in spring and bloom in summer. Adaptable to most well-drained soils; tolerates drought. Full sun.
F. japonica (Polygonum cuspidatum, Reynoutria japonica). JAPANESE KNOTWEED. From eastern Asia. Tough, vigorous plant with wiry, reddish brown stems that form large clumps to 48 ft. tall. Pale green leaves are nearly heart shaped, to 5 in. long. Showy clusters of greenish white flowers appear in leaf axils in late summer and fall. Spreads rampantly by underground runners and is particularly hard to control: Shoots have been known to push up through asphalt. Good choice for bank cover or erosion control in difficult areas where little else will grow. Full sun or partial shade. 'Crimson Beauty' bears fiery red flowers on 7- to 8-ft. stems from late summer through fall; it is known to some Southerners by the name kiss-me-at-the-gate. It's better behaved than the species, forming clumps that are not invasive. F. j. compacta 'Variegata' is less invasive than the species, but if in doubt, treat it like mint and keep it in a container.