- Name also: Grass Rush, Grassy Rush, Water Gladiolus
- Family: Flowering Rush Family – Butomaceae
- Growing form: Perennial herb. Water plant. Rootstock horizontal, creeping.
- Height: 60–120 cm (25–50 in.). Stem round.
- Flower: Corolla regular (actinomorphic), white–light red, red-veined, 2–2.5 cm (0.8–1 in.) broad; petals and sepals 3 (easily looks 6-petalled). Stamens 9, red. Gynoecium base fused, 6 fused carpels, styles 6. Inflorescence a 10–40-flowered umbel.
- Leaves: At base, alternate, stalkless, 40–80 cm (15–32 in.) long. Base sheath-like. Blade linear, cross-section 3-edged, with entire margins, rigid, with tapered tip, alternate at tip. Submerged leaves soft, up to 120 cm (50 in.) long.
- Fruit: Follicle.
- Habitat: Lakes, rivers and low-salt brackish springs, usually in shallow water with a clay or sludge bottom. In deeper water a flowerless submerged plant.
- Flowering time: June–August.
Flowering rush in bloom is an impressive sight, which those who get to admire are ready to say is one of the most beautiful plants in Finland. It is abundant only on rich bird-islands in western Finland and estuaries in Ostrobothnia, where its stands are often broad and dense. Despite its abundance on river banks and in estuaries, however, it can still be hard to spot due to its short flowering time. In fast-flowing water its floppy leaves remain submerged and well hidden from view. Flowering rush has been found in all of Finland’s provinces, but it is quite rare along coasts and in the north and east, and it often flowers only sparsely and occasionally.
Flowering rush’s inflorescence usually only has only a few flowers open at any given time, but over the couple of months that it is in bloom it is able to produce 30 or 40 flowers. The flowers secrete drops of nectar, pollen is produced in abundance and they have a lot of insect visitors, mainly beetles. Finland’s summer can end a bit early from flowering rush’s point of view, because the fruit is rarely able to ripen its seeds. Sometimes poor seed production happens because the plant cannot be fertilised by its own pollen, and it can be that the whole stand in a lake has come from a single plant.
Flowering rush is undoubtedly at its most impressive when it is flowering, but it is possible to differentiate sterile plants too from other wetland herbs because its leaves are 3-edged and their tips are often specially alternate. Particularly in windy weather it is possible to identify flowering rush because its leaves don’t really bend in the wind but rather twist around their longitudinal axis.
“Flowering rush infestations can displace native vegetation and result in reduced water quality which may disrupt valuable fish and wildlife habitat. Dense stands in irrigation ditches can reduce water availability, and in lakes can can interfere with boat propellers and swimming.”
Alberta Invasive Plants Council