Water spinach

A semi-aquatic trailing herb, sprawling on the water surface or spreading on land. The stem is hollow, fleshy, with milky sap, 2–3 m long, rooting at the nodes where it touches mud or water, which keeps the plant afloat and promotes branching. Leaves are alternate, the blade varying from arrowhead-shaped (sagittate) to lanceolate or hastate, 5–15 (to about 17) cm long with petioles 3–14 cm, surfaces glabrous. Flowers are funnel-shaped, 3–5 cm across, usually white with a pale purple throat, borne singly or one to two per stalk. The round capsule is about 7–9 mm across, four-loculed, holding four rusty, hairy seeds.

According to Plants of the World Online (Kew), Ipomoea aquatica Forssk. has the native range "Tropics & Subtropical Old World to Australia", that is the tropical and subtropical Old World (tropical Asia, tropical Africa) extending to Australia; its native habitats include swamps, ponds, ditches and seasonally flooded fields. The species was widely domesticated and popularised in Southeast Asia (considered the domestication centre), South Asia and East Asia, and has naturalised in tropical America. In Florida (USA) it is on the Federal Noxious Weed List and ranked FISC Category 1 Invasive; in Queensland (Australia) it is also managed as an aquatic invader. In Vietnam it is grown and occurs throughout the lowlands, harvested year-round in warm areas.

Chemically, the main constituent is water (about 92% fresh weight), alongside protein around 3.2%, carbohydrates 2.5–4.4%, fibre about 1.5% and ash. Water spinach is rich in beta-carotene (provitamin A), vitamin C and folate together with the minerals calcium, iron, potassium, magnesium and phosphorus. Its main biologically active group is total phenolics and flavonoids; a 2020 review placed water spinach among the top three aquatic leaf vegetables for antioxidant capacity. Freeze-dried water-spinach powder was reported to have a total phenolic content of about 32 µg/mL and antioxidant activity of 77.25% (2021 study). In polluted water the plant tends to accumulate nitrates and heavy metals, while its leaves are rich in oxalates.

On nutrition and uses, Saikia and colleagues (2023, Frontiers in Nutrition) showed Ipomoea aquatica is rich in minerals, dietary fibre and essential amino acids; Cha and colleagues (2023) compared processing methods and found quick stir-frying retained more antioxidant activity than boiling or wilting. Culinary use in Southeast Asia centres on young shoots stir-fried with garlic, boiled or simmered in soups (notably crab and water-spinach soup in Vietnam), and the plant is also a cheap livestock feed using both stems and leaves. In regional folk medicine it is used as a cooling vegetable, a mild laxative and a source of micronutrients, although most therapeutic evidence remains at in-vitro or animal-study level.

On safety, never eat water spinach raw if it grows in polluted water or is fertilised with fresh manure: larvae of liver flukes (Clonorchis/Opisthorchis), lung flukes (Paragonimus) and roundworms can adhere to the leaves, so it must be washed and thoroughly cooked. People prone to kidney stones should limit heavy consumption because the leaves are rich in oxalates; since the plant accumulates nitrates and heavy metals in dirty water, it should only be eaten when grown in clean water sources. On conservation, the IUCN Red List has not evaluated this species (NE); overall it is not threatened because it is widely cultivated across the tropics, but in some temperate and subtropical regions (Florida, Queensland) it is managed as an aquatic invasive.