Water caltrop

Trapa species
Water caltrop is PROHIBITED MATTER If you see this plant, you must report it to the NSW DPI Biosecurity Helpline 1800 680 244 It is a water weed that forms dense mats blocking waterways. Its leaves can float or grow under the water and it produces nuts with sharp spines.
Family: Lythraceae
Origin: Water caltrop is native to warm temperate parts of Eurasia and Africa.
Habit: Water caltrop is not known to occur in Australia. There is archival evidence that it was grown in Queensland in the late 1800s. Water caltrop prefers temperate climates but can grow in tropical regions. It grows best in slow-moving, fresh water bodies up to 5 m deep. Though usually it is in water bodies such as dams, ponds and lakes between 30 cm and 3.6 m deep. Water caltrop grows best in water with high nutrients, but does not tolerate salinity.
Leaves: Leaves are either submerged or floating. Floating leaves are in rosettes (circular clusters with leaves radiating out), are glossy on top, about 2–3 cm long, oval, triangular or diamond-shaped with saw-toothed edges on stalks that usually have a swollen round bulge (which may be green, pink or red) covered in fine, short hairs underneath. Submerged leaves are feather-like and arranged in whorls around the stems. Stems are submerged, long and unbranched reaching 3.6–4.5 m in length anchored into the mud by very fine roots.
Flowers: Flowers are white with four petals, 8 mm long are located above the water's surface and are present in early summer.
Fruit and Seeds: Fruits are a hard, woody or bony nut with only one seed, brown or black, about 3 cm wide with sharp spines filled with only one seed under the floating leaves. Trapa natans var. natans has 4 spines and Trapa natans var. bispinosa has two spines.
Roots: Roots are up to 8 cm long. Often mistaken for feather-like leaves. Submerged leaves drop off during early stem growth and roots form at the points were the leaves dropped off.
Dispersal: Water caltrop is usually introduced to an area through intentional planting by humans. They produce heavy seeds that are released in winter and quickly sink. Seeds germinate in water over 12°C, usually within the first 2 years, but may stay dormant for up to 12 years. The seeds lose their viability if they dry out. In Trapa nutans, fresh seeds need cold conditions (4°C) for at least 9 weeks to break dormancy. A single seed can produce 10 to 15 rosettes and each rosette can then produce up to 15 to 20 seeds. The barbed seeds can be spread by clinging to waterbirds and other animals, fishing nets and traps, boats, clothing and vehicles that go in the water. Floating parts of the plant break away from the stem. the plant parts are spread by flowing water and by clinging to boats and equipment.
Control: Please do not attempt to treat or dispose of this weed yourself. Report this plant if you see it anywhere in NSW by calling the helpline listed at the top of this page immediately. NSW DPI will lead an initial response for the treatment and disposal of the plant to stop it from spreading. Hand removal, herbicides and mechanical removal have been used to control water caltrop in other countries, but the ability of the seeds to lay dormant for many years makes total eradication very difficult.

 

                   

https://sketchfab.com/3d-models/water-caltrop-trapa-natans-873a455740244618863709fa7712e5ab Much of the information used in this fact sheet came from the Dept of Primary Industries WeedWise website (https://weeds.dpi.nsw.gov.au/Weeds/WaterCaltrop)
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