Arrowheads & Water-plantains
What are they?
Arrowheads and Water-plantains form the family Alismataceae, a group of plants with flowers bearing three sepals and three petals and sometimes with male and female flowers carried separately on the flower spike. Also included here is Flowering-rush, which is closely related but in its own family, the Butomaceae. These plants grow as submerged aquatics or as plants of wet mud. When growing in water, the submerged leaves are often narrower and quite different to the aerial leaves.
Where are they found?
As aquatic plants, these species grow as emergents along still or slow-moving water in ditches, dykes and along main waterways. Some species may also occasionally be found in seasonally flooded land where bare mud is available.
Identification
Flowering-rush is unmistakable when in flower, while Common Arrowhead can readily be told by its leaves, which are shaped like arrow heads. The water-plantains can be tricky and identification relies on careful study of aerial leaf shape, petal shape and precise detail of the style placement.
Common Arrowhead Sagittaria sagittifolia
Native. Scattered around the region and growing as an emergent plant of slow-moving rivers, usually in the mid section of the larger rivers. Flowers July to August. In our region, the arrow-shaped leaves emerging from water are usually diagnostic, though beware the commercially available Broad-leaved Arrowhead (see below).
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Broad-leaved Arrowhead Sagittaria latifolia
(Duck-potato) Introduced from North America as a garden pond ornamental. First recorded from our region in South Norfolk in 2024, perhaps having spread from a nearby garden. Flowers July to August. Closely resembles our native arrowhead species but has much larger and broader leaves.
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Common Water-plantain Alisma plantago-aquatica
Native. Widespread in wet places, growing both as an emergent from standing water and on wet mud. Flowers June to August. Small, three-petalled flowers carried in a large, much-branched head. Petals slightly pointed at the tip; leaves rounded to more or less cordate at the base. Under a hand lens, the style can be seen to be about half way up the side of the fruit.
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shown by red line |
Narrow-leaved Water-plantain Alisma lanceolatum
Native. A rare plant found as small, isolated populations in good-quality wetland sites. Flowers June to August. Small, three-petalled flowers carried in a large, much-branched head. Petals not pointed at the tip; leaves spear-shaped, cuneate at the base. Under a hand lens, the style can be seen to be more than half way up the side of the fruit.
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shown by red line |
Lesser Water-plantain Baldellia ranunculoides
Native. Widespread in wet places, typically on wet mud. Flowers July to September. A low, creeping plant with narrow leaves and relatively large flowers. Flowers may appear white from a distance but are pale pink when seen close up.
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Flowering-rush Butomus umbellatus
Native. Grows as an emergent aquatic plant along the main river systems. Generally rather local, but common along some stretches of the Wensum in Norfolk. Flowers July to September. Petals and sepals somewhat similar, giving the appearance of a six-petalled flower. Easily overlooked hen not in flower, but the leaves often have a fairly distinctive spiralled look.
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Starfruit Damasonium alisma
Native. An extremely rare species in the UK, reduced to just three sites in southern England and the subject of intensive conservation work. Formerly recorded in Suffolk, but not seen in our region since 1957. Favours winter-wet areas that provide bare mud on acidic soils. Flowers June to August. Typically a tiny plant, but msy grow to 30cm. Flowers white, followed by star-like fruits.
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