Most of these perennials are vigorous spreaders with a penchant for conquering new territory, especially in moist, fertile soil. Keep them under surveillance to ensure they don't invade choicer plantings. Blossoms are yellow or white and appear in summer, except as noted.
L. barystachys. Native to eastern Russia and Asia. To 2 ft. high, 1 ft. wide, with narrow, green leaves to 3 in. long. Small white flowers come in foot-long spikes that start out horizontal and gradually turn upright.
L. ciliata. FRINGED LOOSESTRIFE. Zones US, MS, LS, CS; USDA 6-9. Native to northeastern U.S. Erect clump to 4 ft. tall, 2 ft. wide, with narrow, green leaves to 6 in. long. Nodding, 1-in., yellow flowers with red-brown centers appear singly or in loose clusters in upper leaf joints. 'Firecracker' is similar but has reddish leaves.
L. clethroides. GOOSENECK LOOSESTRIFE. Native to China, Korea, Japan. To 3 ft. tall, quickly spreading as wide or wider. Erect stems with pointed, olive-green leaves to 5 in. long. Flower spikes densely packed with tiny white blossoms are 68 in. long, arched like a goose's neck. Extremely aggressive spreader; plant only in confined beds. 'Geisha' has leaves edged in creamy yellow.
L. congestiflora. GOLDEN GLOBES. Zones MS, LS, CS; USDA 7-9. Native to China. Mat-forming plant grows to 4 in. high and 1 ft. or wider. Oval, green leaves to 2 in. long; upturned yellow flowers, in. across, in leafy terminal clusters. Blooms from spring to summer. Good in a rock garden or as ground cover in naturalized areas. 'Eco Dark Satin' has yellow blooms with red centers. 'Outback Sunset' has red-tinged leaves with yellow variegation and yellow flowers with red centers. 'Persian Chocolate' has brownish purple leaves.
L. ephemerum. Native to southwestern Europe. Leathery, gray-green leaves to 6 in. long form a neat clump to 3 ft. tall and 1 ft. wide. Slender clusters of white, -in.-wide, long-lasting flowers. Not invasive.
L. nummularia. CREEPING JENNY, MONEYWORT. Native to Europe; naturalized in eastern North America. Grows 48 in. high and spreads to 2 ft. or more, rooting as it goes. Forms an attractive mat of roundish, light green, 1-in. leaves. Yellow flowers about 1 in. across appear singly in leaf joints. Best use is in corners or containers where it need not be restrained. Also good in rock garden or as casual ground cover. Will spill from wall, hanging basket. 'Aurea' has bright yellow leaves that combine especially well with dark-foliaged plants such as black mondo grass (Ophiopogon planiscapus 'Nigrescens'); it requires a shady location.
L. punctata. YELLOW LOOSESTRIFE. Native to central Europe, Asia Minor. To 3 ft. tall, spreading to 2 ft. or more by underground stems. Narrow, green leaves to 3 in. long are borne in whorls on erect stems; inch-wide yellow flowers, also in whorls, appear on top third of stems. Looks nice in masses or mixed borders. 'Alexander' has leaves with gold edges that fade to cream as the weather warms; it grows less vigorously than the basic species and reaches about 2 ft. tall. 'Golden Alexander', to 2 ft. high and wide, has yellow-edged leaves.