Waterweeds
What are they?
Waterweeds are in the family Hydrocharitaceae and are a very variable bunch. Most of them are submerged aquatic plants and will be well-known to anyone who has stocked a garden pond or fish tank, while others are floating aquatic plants with free-hanging roots that are not bedded into the substrate.
Where are they found?
These are plants of still or slow-moving waterways and are found in ponds, ditches, dykes and similar places.
Identification
Water-solider and Frogbit are distinctive and readily identified. The submerged species can be identified by the arrangement of their leaves and by the leaf shape (especially the tip) and size.
Frogbit Hydrocharis morsus-ranae
Native. Once widespread in waterways but now rare except in parts of the Broads and Fens. Found in non-polluted ditches, dykes and small ponds. Flowers July to August. The white, three-petalled flowers are typical of the waterweed family, but the plant otherwise looks like a very small water-lily, with leaves typically no more than 5cm across.
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Water-soldier Stratiotes aloides
Native and locally common in dykes and ditches in the Broads, formerly in the Fens. Occasional elsewhere as an introduction or garden throw-out. Flowers June to August with only female plants known in the UK and plants spreading vegetatively. The white, three-petalled flowers are typical of the waterweed family, but the plant otherwise looks very unlike the rest of the family, with its slightly succulent, aloe-like leaves. Plants survive submerged below the surface until flowering time, when they rise to the surface. Roots hang free rather than rooting into the mud.
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Canadian Waterweed Elodea canadensis
Introduced from North America and first recorded in the British countryside during the 19th Century. Now by far the commonest waterweed in our region in still or slow moving water of ponds and ditches and particularly common in Broadland. Flowers May to September with only female plants known in the UK and plants spreading vegetatively. The tiny, whitish, three-petalled flowers float at the surface on the end of long, thread-like, white stalks. Leaves in whorls of three to four, blunt-tipped.
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Nuttall's Waterweed Elodea nuttallii
Introduced from North America and mostly found in permanent waterways in the Fens and in Broadland, but also scattered elsewhere. Flowers May to September with only female plants known in the UK and plants spreading vegetatively. The tiny, whitish, three-petalled flowers float at the surface on the end of long, thread-like, white stalks. Leaves in whorls of three to four, sharp-tipped.
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Curly Waterweed Lagarosiphon major
Introduced from South Africa and first recorded in the British countryside during the 20th Century. Still rare and only recorded from a handful of locations but likely to increase. Typically a plant of still waters in ponds. Flowers May to September with only female plants known in the UK and plants spreading vegetatively. Leaves strongly recurved, giving stems a rope-like look; not in clear whorls but either loosely whorled or arranged spirally.
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Holly-leaved Naiad Najas marina
A very rare plant nationally, with the entire UK population being confined to slightly brackish sections of the Norfolk Broads. Although rare, the species can be locally very common, although hard to find as it is a submerged aquatic. Flowers July to August. A very peculiar plant with prickly stems and leaves that could be passed off as a seaweed.
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