Nasturtium officinale (watercress, "Orandagarashi")

Japanese name: オランダガラシ （阿蘭陀芥子）
Scientific name: Nasturtium officinale

[Overview]
A perennial 20–50 cm tall, growing in colonies at the water's edge or in water, with stems that creep or float.
The stems are hollow and spread by producing fibrous roots from the nodes.
The leaves are alternate and odd-pinnately compound, with 1–4 pairs of leaflets.
The terminal leaflet is large and ovate-orbicular, and the lateral leaflets are small and elliptic.
The leaf surface is slightly glossy and the margins are wavy.
The petioles are short.
Racemes at the stem tips bear many white four-petaled flowers 1 cm across.
There are 6 stamens, of which 4 are long and 2 short (tetradynamous), and there are large nectaries at the base of the short stamens.
The fruit is a flattened cylindrical silique 1–3 cm long, containing seeds in two rows.
The seeds are ovoid, about 1 mm, and reddish brown.

[History]
It was introduced to Japan around the 3rd–4th year of the Meiji era.
Plants that were cultivated for food have become naturalized and spread along riverbanks and ditches in various places.

[Uses]
The young stems and leaves, with their distinctive fragrance and pungency, are added to salads or used as a garnish for meat dishes.
They are rich in vitamin C, potassium, calcium, iron and other nutrients.
The seeds are used medicinally.

[Cultivation]
Propagate from seed, by cuttings, or by division.
It prefers sandy soil that is sunny and well drained.
It is cold-hardy but somewhat weak in heat, so in summer move it to a airy place in partial shade.
Watch for freezing in winter.
Water thoroughly when the soil surface begins to dry.
For potted plants, bottom watering with the pot standing in water is also fine.
It also grows well in hydroponics.
With bottom watering or hydroponics, change the water frequently so that it does not spoil.
Apply liquid fertilizer once every 10 days in spring and autumn.
Pests and diseases include downy mildew, viral diseases and aphids.

[Notes]
It is designated as an alien species requiring caution.

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