water mimosa

Neptunia oleracea and N. plena
Aquatic
Opposite
Compound
Yellow
Green

Biosecurity Queensland must be contacted within 24 hours 13 25 23.
Biosecurity Queensland Must attend site before any control measure is administered, advice will be provided to the land holder at this time.

Water mimosa is an aquatic floating perennial herb that attaches to the bank at the waters edge and sends down a taproot. Stems grow out over the water and form a spongy, fibrous covering between the nodes. Fibrous (adventitious) roots grow from the nodes. The rooted land form has smaller leaves and flowers, and has no spongy floating tissue.

Common names 
Also known as: sensitive neptunia,
Family 
Fabaceae
Deciduous 
No
Flowering time 
Summer
Native/Exotic 
Exotic
Origin 
Tropical Asia, Africa and South America
Notifiable 
Yes
State declaration 
Category 2,3,4,5 - Must be reported to Biosecurity inspector or authorised person. Must not be distributed, moved, possessed or kept under your control.
Council declaration 
As per State Declaration
Known distribution 

Found in South East Queensland.

Habitat 

Within its native range, water mimosa is a common floating plant in freshwater pools, swamps and canals at low altitudes of up to 300 m. When water levels fall during the dry season, the plants often perish. The plants prefer slow-moving water 30–80 cm deep, full sun and hot, humid conditions. Shade, brackish water and saline soil adversely affect plant growth.

Habit 

Water mimosa is an aquatic floating perennial herb that attaches to the bank at the water’s edge and sends down a taproot. Stems grow out over the water and form a spongy, fibrous covering between the nodes. Fibrous (adventitious) roots grow from the nodes. The rooted land form has smaller leaves and flowers, and has no spongy floating tissue.

Biosecurity Queensland Must attend site before any control measure is administered, advice will be provided to the land holder at this time
Water mimosa poses an extreme threat to Queensland’s waterways and wetlands. It establishes from small plant pieces in water and from seed. Under favourable conditions, water mimosa grows out from the banks to form floating rafts of dense interwoven stems. These can be dislodged by water movement (especially during floods) and are soon replaced by more water mimosa. These floating rafts can restrict water flow in creeks, channels and drains. It can impede recreational water sports and boating access. The rafts are so dense they can reduce water quality by preventing light penetration and reducing oxygenation of water. This creates favourable habitat for mosquitoes and reduce fish activity, causing the death of native, submerged water plants and fish.

Stem and leaves 

Leaves are olive green and are arranged in opposite pairs along the stem. When disturbed or touched the leaflets close up

Neptunia oleracea stems to 1.5 m long, prostarate at the waters edge, rarely branched, becoming detached from the primary root system, forming a spongy-fibrous indument between the nodes and producing fibrous adventitious roots at the nodes when growing in water.

Neptunia pleana stems to 2 m tall, erect to ascending (rarely prostrate) glabrous or forming a spongy-fibrous indument when in water. Leaves have leaflets 9–38 pairs per pinna, 4.0–14 (–18) mm long, 1–3 (–3.5) mm broad. Leaves have leaflets, 8–20 pairs per pinna

Flowers and fruits 

Neptunia oleracea - flowers, yellow 30–50 per spike and each flower is 7.0–16.0 mm long, 0.5–1.0 mm broad. Seeds are oval and brown, 4–8 per legume. Each seed is , 4.0–5.1 mm long, 2.7–3.5 mm broad.

Neptunia pleana - flowers yellow, 30–60 per spike, 9–16 mm long, 1–1.6 mm broad. Seeds are oval and brown, 8–20 per legume. Each seed is 4.0–4.1 mm long, 2.2–2.3 mm wide.

Reproduction and dispersal 

Because it is an Asian vegetable, water mimosa has been subject to sale and distribution through Asian communities and gardeners. As water mimosa can form floating raf ts of dense inter woven stems, these can be dislodged by water movement (especially during floods) and reestablish further downstream.