Lagarosiphon

Lagarosiphon is on the Alert List for Environmental Weeds, a list of 28 nonnative plants that threaten biodiversity and cause other environmental damage. Although only in the early stages of establishment, these weeds have the potential to seriously degrade Australia’s ecosystems. 

Lagarosiphon is an aquatic plant that can dominate freshwater lakes, dams and slow-moving streams. It grows extremely quickly from the bottom of a water body to the surface and forms dense mats several metres thick at or just below the water surface. These mats stop light from penetrating into the water and displace native vegetation. Dense infestations can also deplete oxygen in the water. Infestations of lagarosiphon choke waterways and reduce the potential for recreational use (eg fishing, boating) and commercial exploitation (eg by blocking water intakes for hydro-electricity). It is a major water weed in parts of Europe and New Zealand. In the past it has been found and eradicated from a few small dams in southern Australia.

Lagarosiphon reaches its maximum growth in clear water up to a depth of 6.5 m, but may only grow to 1 m in murky water. It has numerous threadlike roots which are ‘adventitious’ (branching from the stem) and, along with rhizomes (horizontal stems in the sediment), anchor it to the bottom. Stems, which can reach the surface, are brittle and sparsely branched, 3–5 mm in diameter and curved towards the base (J-shaped). The leaves are 5–20 mm long and 2–3 mm wide, and occur in alternate spirals along the stem. They generally have tapered tips curving downwards towards the stem, except in low alkalinity water where they are straight