Dark green submerged aquatic plant, scarcely branched, with small alternated and curved-down leaves, closer joint near the apex. It forms “tufts” at the bottom of the water body, and can grow up to 6 meters tall, forming surficial floating “carpets”.
Scientific name: Lagarosiphon major (Ridley) Moss
Common name: African elodea, African curly leaved waterweed, African oxygen-weed, African waterweed, coarse oxygen weed, curly water thyme, curly waterweed, fine oxygen weed, Lagarosiphon, oxygen weed, oxygen-weed, South African oxygen weed, submerged onocotyledon
Family: Hydrocharitaceae
Status in Portugal: Invasive species (listed in annex II Decree-Law no. 92/2019, 10th July). Included in the list of species of concern in the European Union, by Regulation (EU) no. 1143/2014 of the European Parliament and of the Council of October 22, 2014. Introduced in some points, it is already showing invasive behaviour, although with still relatively limited distribution.
Risk Assessment Score: [In developement]
Synonymy: Lagarosiphon muscoides var. major Ridl. It is often sold under the name Elodea crispa, although this scientific name does not exist.
Last update: 13/06/2020
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How to recognise it
Dark green submerged aquatic plant, little branched, with small leaves alternated and curved down and closer together near the apex. It forms “tufts” at the bottom of the water, and can grow up to 6 meters, forming floating “carpets” close to the surface.
Leaves: dark green, pointed and finely toothed, 5-20 mm long and 2-3 mm wide. They are arranged alternately, in a spiral, around the stem and are generally curved downwards towards the stem, (but in alkaline waters, they may appear straight). They usually appear closer together near the apex.
Stem: brittle and sparsely branched, it can grow to over 6 meters in length and curves like a “J” towards the base. It has adventitious roots and rhizomes that fasten the plant to the substrate.
Flowers: the female flowers are very small, with 3 transparent, white or pink petals and are situated above the surface, attached to a thin and long filamentous peduncle.
Outside its native range, only female plants are known, but in South Africa, where it originates, male plants produce flowers that detach from the plant, floating freely to disperse pollen.
Similar species
Hydrilla verticillata, Egeria densa, Elodea canadensis
The three species look very similar but the number of leaves that unite at each node is different; see the illustrated key to see how they are distinguished. Or download the PDF [here]
Characteristics that aid invasion
Although it does not reproduce sexually in Europe (no male flowers, fruits or seeds are known outside its Native range), it reproduces effectively vegetatively, either by expansion of the rhizomes or by fragmentation. Small fragments can be carried by the current in rivers and be accidentally dispersed by boats, fishing artifacts or other human activities and each fragment can give rise to a new plant.
The fact that herbivorous animals (such as fish, waterfowl, invertebrates, etc.) generally prefer native plants can lead to their progressive elimination in places with the presence of exotic oxygenating species (e.g. Lagarosiphon major, Egeria densa, and Elodea canadensis). For this reason, it is common for only exotic species to remain, forming monospecific communities (with only one species).
Native distribution area
South Africa.
Distribution in Portugal
Beira Litoral (Coimbra) and Algarve (Odeleite).
For more detailed locations of this species, check the online interactive map. This map is still incomplete – we need your help! Contribute by submitting records of the location of the species where you can find it.
Other places where the species is invasive
Europe (Austria, France, Germany, Italy, Spain, Switzerland and the United Kingdom), Oceania (New Zealand).
Introduction reasons
The main reason for its introduction is its use in aquariums as an ornamental and oxygenating plant.
Preferential invasion environments
Lagarosiphon major prefers still or slow-current freshwater habitats, with muddy or sandy substrates. It occurs in both oligotrophic and eutrophic environments and has great tolerance to high pH waters. It prefers temperatures ranging between 20ºC and 23ºC, but tolerates winter and supports maximum temperatures of 25ºC (Kasselmann 1995). It only occurs up to 7 meters deep because it cannot withstand higher pressure, but in deep habitats it can form floating mats. It can colonize ponds, lakes, dams, reservoirs and rivers and slow-current canals.
