African elodea
Native to: Africa
It has not yet been documented in the United States but as a member of the Hydrocharitaceae family (along with the present and highly invasive Hydrilla verticillata), African elodea was proactively added to the federal noxious weed list due to the problems it could cause if introduced and established. Introduced outside its native range via the aquarium trade it is problematic in New Zealand and parts of Europe.
Family: Hydrocharitaceae
Habit: Submersed, long-stemmed aquatic perennial.
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/Seeds: Capsule is beaked; seeds 1/8 in. long, averaging nine to a fruit.
Distribution in Florida: Not present
Outside its native range, only female plants are known and thus reproduction is only by vegetative fragmentation. However, it grows rapidly and can form dense 6.5 to 10 feet thick. Its impacts are similar to those of Hydrilla – it displaces native plants and reduces biodiversity, decreases water quality, and impedes recreational activities.
Always clean boats and equipment before leaving a waterbody. Transporting plant fragments on boats, trailers, and in live wells is the main introduction route to new lakes and rivers.
Hand pulling would require complete removal of all plant fragments to be effective.
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)
Chinese grass carp has a moderate feeding preference for Lagarosiphon major (Edwards 1975; Chapman & Coffey 1971)
Fluridone was ineffective when used in a New Zealand lake (Wells & Coffey 1984). With Diquat, “only minimal herbicidal effects” were noted and so several formulations of diquat were deemed ineffective against it 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).
