Neptunia oleracea
Common Name: water mimosa
Type: Herbaceous perennial
Family: Fabaceae
Native Range: Pantropical
Zone: 9 to 12
Height: 0.25 to 0.50 feet
Spread: 1.00 to 5.00 feet
Bloom Time: June to September
Bloom Description: Greenish-yellow
Sun: Full sun to part shade
Water: Wet
Maintenance: High
Suggested Use: Water Plant, Rain Garden
Flower: Showy

Culture

Winter hardy to USDA Zones 9-12. Can be grown as an annual. Best sited in full sun to part shade. Set out plants in spring after the last frost date at a point when water temperatures have risen to at least 70 degrees F. Plants may be grown in containers. Site plant roots along water margins of small ponds or water gardens (with some water over the crowns and with stems extending out into the water) or float plants directly on the water. If overwintering is desired, bring plants indoors in fall to an aquarium when outside fall temperatures dip to 50 degrees F. Propagate by stem cuttings.

Noteworthy Characteristics

Neptunia oleracea is a pantropical nitrogen-fixing perennial legume that is primarily found growing prostrate in wet soils near the water's edge or floating on the water in relatively still-water areas. Floating plant stems often form thick foliage mats. Aerenchyma (white spongy air-conducting tissue that gives stems buoyancy) forms on stems floating in water, but does not form on stems growing on land. Plants typically grow to as much as 6" tall, but stems will spread in the water to 3-5' long. Stems are clad with bi-pinnate, fine, mimosa-like leaves that close up when touched (hence the sometimes used common names of water sensitive plant or water mimosa). Primary leaf segments have 8-40 small oblong leaflets arranged in opposite pairs. Tiny greenish-yellow flowers are densely crowded into feathery orbicular inflorescences that bloom in summer. Fruits are flat pods (to 1-2" long). This plant is considered to be an invasive aquatic weed in some tropical waters where large mats may form that choke waterways, resulting in restricted water flow, reduced water quality, reduced fish activity and loss of some underwater and native wetland plants. The native habitat of Neptunia oleracea is unknown, but some experts believe it is in the area of Mexico to northern South America. This plant is cultivated as a vegetable in southeast Asia (leaves and shoots have cabbage-like flavor).

Genus name comes from the Latin word Neptunus for Neptune, god of the sea, rivers and fountains in allusion to its watery habitat.

Specific epithet means of the vegetable garden.

Problems

No serious insect or disease problems. Plants can be invasive in semi-tropical to tropical areas.

Garden Uses

Where winter hardy, this neptunia adds interest to small ponds and water gardens. May be grown as an annual. Also grows well in aquariums or greenhouse ponds.