Nasturtium microphyllum aka Onerow Yellowcress

Nasturtium microphyllum belongs to the cabbage family, Brassicaceae. It is a perennial, so it lives for more than two years. People call it narrow-fruited watercress or onerow yellowcress. Its native range spans Europe to the western Himalaya. It also grows as a native in Morocco and Ethiopia. Southwest Arabia and Australia form part of this range too. The RHS lists it as native to Britain and Ireland. It grows where the climate is temperate, along streams and ditches. It also grows in wet flushes, often over chalk or limestone. Moving water is key to its habitat.

Plants reach about 1.6 feet (0.5 metres) tall. They spread to about 3.3 feet (1 metre) wide. This size suits shallow pond edges and bog gardens. Each flower has both male and female parts. Bees and flies help the flowers set seed through pollination. Plants are self-fertile: they can set seed with their own pollen. The supplied sources give no flower colour or bloom season. They give no detailed account of leaves or fruit either.

The plant grows best in clean water that moves slowly. Water about 0.16 feet (0.05 metres) deep suits it. It needs clean water, since pollution can harm it. It grows in sand, loam or clay soils. It accepts soil that is mildly acid or mildly alkaline. Neutral soil suits it too. PFAF gives 7.2 as the best pH. You can also grow it in wet soil. This calls for some shade and protection in winter. Yet PFAF otherwise says it cannot grow in shade. PFAF reports hardiness to about −15°C and USDA zones 5–9.

People grow this watercress for leaves they can eat. Eat them raw or cooked, in salads or as garnishes. Their strong, hot taste may grow stronger in wet soil. The leaves provide vitamins and minerals, such as iron. You can eat seed sprouts or grind seeds for a mustard-like seasoning. Cold water brings out the heat in ground seed. PFAF lists no known hazards but urges care with use as medicine. It notes past uses for coughs, digestion and other complaints. These records do not prove that such treatments work.

Seed sown in spring can sprout within about two weeks. Start with pots partly under water. Then raise the water level a little at a time. Move young plants into a pond in summer. Cuttings form roots during the growing season. Even a leaf that breaks off may root in water. Take care when moving plant pieces, since they root with ease. PFAF warns it may become a weed. It gives no details of where it may spread and invade.