Ipomoea aquatica (water spinach, "Yosai")

Japanese name: ヨウサイ （蕹菜）
Scientific name: Ipomoea aquatica

[Overview]
A climbing perennial thought to be native to Southeast Asia.
It is susceptible to cold, so in Japan it is treated as an annual.
It prefers wet, marshy places and also grows in very moist soil.
The stems are hollow and creep along the ground, growing 2–3 m or more in length and rooting at the nodes; they also float on the water and spread across the surface.
The leaves are alternate, 3.5–17 cm long and 1–8.5 cm wide, and vary from arrowhead-shaped to elliptic-ovate, long triangular and lanceolate, with pointed tips.
The leaf margins are entire or wavy.
The flowers are borne 1–5 at a time in the leaf axils; they are funnel-shaped, 3.5–5 cm across, and resemble those of the morning glory (Asagao).
They are white, pink or pale purple, usually with a dark reddish purple center.
The fruit is an ovoid to spherical capsule about 1 cm across.
In Japan it rarely flowers when grown outdoors, and even when it flowers it hardly ever sets fruit.

[Uses]
The stems and leaves are used as a vegetable and also medicinally.
It is sometimes grown in lakes and ponds in the hope of purifying the water.

[Cultivation]
Propagate from seed or by cuttings.
Cuttings root easily even if simply placed in water.
It likes heat and humidity; the optimum temperature for germination is 22°C or higher and for growth 25–30°C; growth stops below 10°C, and frost kills it.
It prefers a sunny, well-ventilated place and fertile soil that is well drained yet retains water.
Because it is a waterside plant, water thoroughly as soon as the soil surface begins to dry so that it never runs short of water.
For harvesting, cut off the soft upper part of the stem and then apply additional fertilizer; side shoots then appear one after another, and harvesting can continue until autumn.
Pests and diseases include thrips, sweet potato leaf miner moths, cutworms, aphids and spider mites.

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