Starry Stonewort (Nitellopsis obtusa)

Key Identification Features

• Star-shaped oogonium

• Branching whorls

Description

Starry Stonewort is an invasive macroalgae that grows in fresh to slightly brackish water. N. obtusa has a “gelatinous” bright green coloration. It has long, irregular branchlets that extend out in whorls of 4-6 from a stem node. Starry stonewort can grow up to 2m in the water column, forming dense mats. When crushed, starry stonewort has no distinctive smell, most often smelling like the lake, whereas native macroalgae (Chara spp. & Nitella spp.) have distinctive smells.

In early summer starry stonewort forms the star-shaped, white oogonium for which it is named. Orange to red oocytes are also produced along the stem nodes.

Native Range

Starry Stonewort is native to Eurasia and found from Europe’s West coast to Japan.

Habitat and Dispersion

Starry stonewort prefer slow moving water and can tolerate up to 5% salinity.

Best Management Practices

Prevention is the best way to manage starry stonewort. Once introduced to a waterbody it spreads easily through fragmentation and is hard to fully eliminate. Benthic mats can be deployed around docks and access areas to limit its growth.

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Additional Resources

USGS

NYSDEC

W-NY PRISM