Lagarosiphon major

African elodea

Not Present in FloridaFederal Noxious Weed List

Species Overview

Elodea crispa (by those who keep aquaria (Mason 1960)

Happily, Lagarosiphon major does not yet occur in the wild in the United States, as 2008, so far as is known. However, experts have reason to believe that should this plant be introduced to the U.S., the resulting problems could be as consequential as those caused by another plant in the Hydrocharitaceae family, hydrilla (Hydrilla verticillata)

  • Lagarosiphon major is native in southern Africa
  • there are about 15 other species of Lagarosiphon native in southern Africa, Madagascar and India

Species Characteristics

Lagarosiphon major (Ridley) Moss ex Wager
Original description: Trans. Proc. Roy. Soc. S. Africa 16(2):191-201. 1928.

  • monocot
  • rooted in the hydro-soil by numerous thread-like unbranched roots
  • stems submersed; brittle; 3 mm (1/8 in.) in diameter; growing to 20 feet long; branching every 10-to-12 nodes; reaching the surface to spread into thick mats
  • leaves submersed; greatly recurved; stiff; alternate spirally along the stem; leaves linear to linear-lanceolate; to 16 mm (1 in.) long by 2 mm (1/16 to 1/8 in.) wide; leaves 3-veined with visible midvein; leaf margins minutely toothed; at stem tips, leaves are very densely crowded
  • flowers tiny, transparent to white or pinkish; all parts in 3’s; in its native range, female flowers reach the surface on long thread-like tubes (to 10 in. long); on the surface they bump into and are pollinated by free-floating male flowers (Cook 1987); male flowers form in the leaf axils, after which they rise to the surface where they sail about; staminate spathes enclose many flower buds, carpellate spathes enclose only one flower (Haynes 1988)
  • fruit capsule is beaked; seeds 1/8 in. long, averaging nine to a fruit
  • outside its native range, only female plants are known and thus reproduction is only by vegetative fragmentation

As a submersed, long-stemmed plant having many small narrow leaves, Lagarosiphon major might be confused with three other plants in the U.S. As chance would have it, two of these three other plants are themselves also not native to the U.S.; however they are here, whereas Lagarosiphon is not (early 2008).

It is believed that this plant was in New Zealand for some time before it was recognized as a plant distinct from Elodea canadensis in the 1950s. By the time it was recognized, Lagarosiphon major was already a major weed there. (Healy)


  • Lagarosiphon major is fast-growing
  • may totally fill the volume of a large shallow lake (to 3 m deep)
  • fills water control channels
  • in New Zealand, Lagarosiphon major is a major aquatic weed problem recorded in many lakes
  • in England, this plant was reported in 1976 as being “well established in scattered localities in the south, now, two decades later, Lagarosiphon major is “actively displacing” Elodea species in “some lentic British waters” (James, Eaton & Hardwick 1998); it was first recorded in England in 1944 (Silverside and Raymond 1976)
  • “within two years of the first record of L. major in the boat harbour it had largely replaced E. canadensis there” (Coffey 1975)
  • within 13 years from its first record on the lake, the plant occupied almost all of the 161 km length of the littoral zone (Howard-Williams 1988)
  • in New Zealand lakes, this plant has attained biomass weights of 165-424 g m2 dryweight; if this plant, like hydrilla, is 99% water, then the weight of the plant as an infestation in the water is in the range of 16500-42400 g m2 (which converts to 88-225 tons of plant biomass per acre)
  • heavy booms protecting hydro-electric power plants’ water intake units “fail when a massive amount of weed is liberated after storms” (Chapman 1974)
  • with its canopy spreading across the top part of the water, it is able to shade out and thus outcompete other submersed species; 1% light level occurs through as little as .5 m of Lagarosiphon biomass (Schwarz and Howard-Williams 1993) (only 1% of the sunlight can pass through as little as 1.5 ft of a Lagarosiphon infestation)
  • in spite of one of its common names, oxygen weed, in a dense infestation of Lagarosiphon major there often is less oxygen present than in the surrounding water: thus dense infestations, “in such quantities confer no oxygen benefit on fish and other animals in the lake” (Chapman 1974)
  • Lagarosiphon major caused a power outage in 1968 when it blocked the intake screens at Aratiatia hydro station in New Zealand
  • the plant is detrimental to recreation in Hamilton Lake and Lake Rotorua, New Zealand

Control Methods

Preventive Measures

First, clean your boat before you leave the ramp. Transporting plant fragments on boats, trailers, and in livewells is the main introduction route to new lakes and rivers.


the action of mechanical harvestors and chopping machines causes fragmentation, which helps spread Lagarosiphon major; “if the weed is cut in mid-summer, the infestation (1m or 6 m) is completely restored by the fall” (Chapman 1974)


the herbivorous (plant-eating) biological control fish, the Chinese grass carp, has a moderate feeding preference for Lagarosiphon major (Edwards 1975; Chapman & Coffey 1971)


the aquatic herbicide fluridone was deemed ineffective when used against Lagarosiphon major in a New Zealand lake (Wells & Coffey 1984); as for another aquatic herbicide, diquat, “only minimal herbicidal effects” were noted and so several formulations of diquat were deemed ineffective against the plant in New Zealand streams (Tanner & Clayton 1984) and diquat “is not effective in turbid water” (Clayton 1998); on the other hand, diquat applications are believed to have affected this plant’s growth in Lake Rotoroa (Tanner & Clayton 1990); sodium arsenite herbicide effects on this plant were described as “spectacular” in 1960, but 24 years later, high arsenic levels persisted in soil and plants (Tanner & Clayton 1990), and “little of the original arsenic applied for weed control was lost from the lake between 1959 and 1992” (Clayton & Tanner 1994)