Sagittaria sagittifolia aka Arrowhead

Sagittaria sagittifolia, or arrowhead, is a wetland perennial in the Alismataceae family. Its native range runs from Europe to Siberia and the Caucasus. It is native to Britain and Ireland. The plant grows in ponds, canals, and streams with slow flow. Mud beneath fresh water provides its rooting ground. It suits pond edges, bog gardens, and wildlife gardens.

Garden plants reach about 1.6–3.3 feet [0.5–1 metre] tall. Their spread reaches 3.3–4.9 feet [1–1.5 metres]. They take two to five years to reach full size. The plant has an upright form and loses its leaves seasonally. Leaves held above water have the arrow shape behind its name. Those that float on the surface are oval. Leaf stalks can reach about 1.5 feet [0.45 metres] long. Slender underground roots bear starchy tubers at their ends. These can lie some distance from the parent plant.

Flower stems rise to about 2.6 feet [0.8 metres]. They carry blooms in July and August. Each flower measures about 0.1 feet [0.03 metres] across. Three white petals have purple marks at their bases. The blooms stand above the water on upright spikes. Together, the flowers and distinct leaves give ponds seasonal interest. The foliage dies back as the growing season ends.

Grow arrowhead in sun or partial shade, in a sheltered spot. It needs deep mud and still or slow-moving fresh water. RHS advises water depths up to 0.7 feet [0.2 metres] for cultivation. Wild habitats include water around 1.5 feet [0.45 metres] deep. Clay and loam suit it, with acid, neutral, or alkaline conditions. RHS rates it H6; PFAF lists USDA zones 6–9. Plants need no pruning and have few pest or disease problems. Propagate them through seed, division, or stolons. PFAF flags weed potential, so spread deserves attention in small ponds.

PFAF lists the leaves and tubers as edible plant parts. Its food guidance centres on cooked tubers, which taste somewhat like potatoes. Do not eat the tubers raw. Remove their bitter skins after cooking. Dried tubers can also yield flour for bread or gruel. PFAF records traditional medicinal uses, but these do not establish safe treatment. It warns that tubers may trigger premature birth. This caution matters despite its separate entry reporting no known hazards.