Description
Young plants initially start with a seedling stem with roots growing in mud at the bottom of the water; further adventitious roots are produced at intervals along the stem, which may hang free in the water or anchor into the bottom. It grows indefinitely at the stem tips, and single specimens may reach lengths of 3 m (9.8 ft) or more.
The leaves are bright green, translucent, oblong, 6–17 mm long and 1–4 mm broad, borne in whorls of three (rarely two or four) round the stem. [6] It lives entirely underwater, the only exception being the small white or pale purple flowers which float at the surface and are attached to the plant by delicate stalks.These stalks, or hypanthia, are the lower part of the petals joined to form a floral tube. This floral tube can be up to 30 cm (12 in) in length, while only 1 mm in width, [7] for a length to width ratio of 300 fold. However, according to one article, this ratio can sometimes be as much as one thousand fold. [8]
It is dioecious, with male and female flowers on different plants. The flowers have three small white petals; male flowers have 4.5–5 mm petals and nine stamens, female flowers have 2–3 mm petals and three fused carpels. The fruit is an ovoid capsule, about 6 mm long containing several seeds that ripen underwater. The seeds are 4–5 mm long, spindle-shaped and smooth. It flowers from May to October. [3] [4] [5] [9]
It grows rapidly in favorable conditions and can choke shallow ponds, canals, and the margins of some slow-flowing rivers. It requires summer water temperatures of 10–25 °C and moderate-to-bright light levels. [9]
It is closely related to Elodea nuttallii , which generally has narrower leaves under 2 mm broad. It is usually fairly easy to distinguish from its relatives, like the Brazilian Egeria densa and Hydrilla verticillata . These all have leaves in whorls around the stem; however, Elodea usually has three leaves per whorl, whereas Egeria and Hydrilla usually have four or more. Egeria densa is also a larger, bushier plant, with longer leaves. [10]
As an invasive species
It is an invasive species in Europe, Asia, Africa, and Oceania. Europe has been particularly affected, with the first records dating back as far as 1836 in County Down, Ireland, and in Great Britain in 1841; [12] [13] it is now abundant in both Ireland and Great Britain. [14] The species' presence has been confirmed in all continental European countries, [15] spreading through ponds, ditches and streams, which were often choked with its rank growth. [16] [9] [10]
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