Sium suave aka Water Parsley

Sium suave has two names: water parsnip and water parsley. It belongs to Apiaceae, the carrot family. This perennial lives for more than one year. It grows in temperate regions, where the climate is mild. Its native range spans temperate Asia and subarctic North America. That range extends into the United States. In North America, it grows in swamps and wet meadows. It also grows in wet woods and by streams. Other sites include ponds, ditches, and muddy shores. It is not native to Britain or Ireland.

Plants grow upright to 2–6 feet (0.61–1.83 metres) tall. They spread 2–3 feet (0.61–0.91 metres) wide. A thick, hollow main stalk bears deep green leaves. The leaves are pinnate, with leaflets set along a stalk. Each leaf is about 0.33–0.83 feet (0.10–0.25 metres) long. Each has seven to seventeen leaflets with toothed edges. The leaflets have sharp tips and a lance shape. They can reach 0.33–0.42 feet (0.10–0.13 metres) long. Leaves below water differ from those above the surface. Their fine parts look like threads. Keep this difference in mind when viewing plants in shallow water.

Tiny white flowers stand out above the green leaves. Chicago Botanic Garden gives July through October as the bloom time. The blooms make a showy feature in wet sites. The upright form suits use as a specimen plant. Its height suits groups of taller wetland plants, too. Grow it in water gardens or at pond edges. It also suits native plant beds where soil stays wet.

Grow water parsnip in full sun or part shade. Keep the soil moist to wet while it grows. It can grow in shallow standing water as well. It thus suits sites where the soil stays moist. Chicago Botanic Garden lists USDA hardiness zones 4–7. Missouri Botanical Garden rates its care needs as medium. Plants may grow from their own dropped seeds where conditions suit them. Divide the rootstock in early spring to grow more plants. Missouri Botanical Garden reports no serious insect or disease problems.

People have boiled the roots to eat as a vegetable. But Missouri Botanical Garden warns against eating this plant. It looks much like Cicuta maculata, the extremely poisonous water hemlock. This makes it unsafe to gather for food. The warning stems from the risk of mistaking one for the other. It does not show that water parsnip itself is poisonous. Treat the past food use as a warning. Do not take it as advice to harvest the plant.