Invasive species fact sheets

Invasive aquatic plants


Starry Stonewort (Nitellopsis obtusa)

Starry stonewort fact sheet
Starry stonewort watch card
Starry stonewort lookalikes

What is starry stonewort?

Starry Stonewort
Starry stonewort pulled from Minnesota's Lake Koronis

Starry stonewort are grass-like algae that are not native to North America. The plant was first confirmed in Minnesota in Lake Koronis, near Paynesville in Stearns County, in late August of 2015. Plant fragments were probably brought into the state on a trailered watercraft from infested waters in another state. In August of 2016, starry stonewort was confirmed in several north-central Minnesota lakes in Beltrami, Itasca and Cass counties. DNR invasive species staff found that a number of other reports of suspected infestations were native species that appear similar to starry stonewort.

How to identify starry stonewort?

Starry stonewort is similar in appearance to native grass-like algae such as other stoneworts and musk-grass. Native stoneworts and musk-grass are both commonly found in Minnesota waters. Starry stonewort can be distinguished from other grass-like algae by the presence of star-shaped bulbils.

If you suspect you have found a new infestation of starry stonewort, or any other invasive species, note the exact location, take a photo or keep the specimen, and contact the DNR.

Why is starry stonewort a problem?

Starry stonewort can interfere with recreational and other uses of lakes where it can produce dense mats at the water's surface. These mats are similar to, but can be more extensive than, those produced by native vegetation. Dense starry stonewort mats may displace native aquatic plants.

Like all plants, starry stonewort may grow differently in different lakes, depending on many factors. At this time, we cannot predict how it might grow in any one Minnesota lake.

How does it spread?

Starry stonewort is believed to be spread from one body of water to another by the unintentional transfer of plant fragments and bulbils, the star-like structures produced by the plant. These fragments, or mud containing them, can be transferred on trailered boats, personal watercraft, docks, boat lifts, anchors or any other water-related equipment that is not properly cleaned.

What can people do to prevent its spread?

The most important action you can take to limit the spread of starry stonewort and other non-native aquatic plants is Clean, Drain, Dispose. Clean all vegetation, animals, mud and debris from your watercraft and any water-related equipment before you move it from one body of water to another. Drain all water from your watercraft and bait bucket, keep drain plugs out during transport, and Dispose of any unwanted bait in the trash. Clean, Drain, Dispose is required by law in Minnesota.

What can be done to reduce starry stonewort?

The potential to manage the plant is not well documented. It appears that treatment with herbicides can suppress starry stonewort. Some states use hand pulling, which may be a way to reduce biomass in small areas. Mechanical removal can also be effective. In the case of a newly discovered population of starry stonewort that has a limited distribution in the lake, mechanical harvesting is not recommended because it might create fragments that would speed the spread of the invasive plant within the lake.