starry stonewort

Starry stonewort is an invasive green alga that has spread rapidly within some northern-tier lakes. It can grow tall and dense, forming mats on the surface that interfere with recreation and potentially displacing native plant species. MAISRC researchers are currently performing ecological niche modeling to assess risk of spread in Minnesota as well as laboratory experiments to assess how long it can survive out of water and to evaluate the efficacy of herbicides and algaecides while minimizing non-target impacts. Click here to download a factsheet about starry stonewort research at MAISRC.

About starry stonewort

What it is 

The scientific name for starry stonewort is Nitellopsis obtusa. It is a type of freshwater green algae known as a charophyte, a group that also includes muskgrasses and stoneworts (Chara and Nitella species) that are native to Minnesota. Starry stonewort is native to parts of Europe and Asia. It is relatively uncommon in much of its native range and is considered endangered in Japan and of conservation concern in Britain.

Life cycle

Starry stonewort is dioecious, meaning that individuals are either male or female — unlike many plants and algae that have both male and female reproductive parts. Interestingly, the best evidence to date indicates that the populations in the U.S. are all male, though there may be undiscovered females. This means that spread of starry stonewort is probably through human movement of fragments from lake to lake. In particular, starry stonewort produces small, star-shaped structures called “bulbils” that allow it to reproduce vegetatively (clonally).

What it affects

Where starry stonewort grows densely and forms surface mats, it can interfere with boating and other recreational activities. Dense growth may also displace native plants and could potentially have impacts on fish and other animals. Starry stonewort’s ecological impacts are not well understood, and there has been little published research to date.

What it looks like

Starry stonewort can look quite similar to some native charophytes, but may appear larger and more robust. It is a green macroalga with whorls of long, narrow branchlets in groups of 4 to 6 coming off of main shoots. Orange reproductive structures (male antheridia) occur at branchlet nodes. Small, white, star-shaped bulbils are a distinguishing feature that gives it the name starry stonewort.

Where it's found

Starry stonewort was first found in North America in 1978 in the St. Lawrence River and has spread inland since. It is now found in much of Michigan’s Lower Peninsula and many locations in New York State. It has also been found in Indiana and was discovered in southeastern Wisconsin in 2014. It was first recorded in Minnesota in 2015 (Lake Koronis, Stearns Co.).

How it spreads

Starry stonewort appears to be spreading vegetatively in the U.S. (by bulbils and fragments). Accidental movement by people is the most likely means of dispersal. Many of the known infestations occur in high-use waterbodies and near boat accesses.

starry stonewort

starry stonewort

Starry stonewort research at MAISRC


Completed efforts

  • Performed ecological niche modeling to predict areas vulnerable to future invasion
    • Used data on where starry stonewort occurs in its native and invaded ranges — and climate and environmental data associated with those occurrences — to predict areas of suitable habitat where it could potentially invade and persist if introduced
    • Found that starry stonewort is occupying a climate niche in its invaded range distinct from the climatic conditions under which it occurs in its native range
    • Substantial portions of the U.S. with no known occurrences of starry stonewort may be at risk of future invasion
    • Escobar, L. E., H. Qiao, N. B. D. Phelps, W. D. Pearse, C. K. Wagner, and D. J. Larkin. In press. Realized niche shift associated with the Eurasian charophyte Nitellopsis obtusa becoming invasive in North America. Scientific Reports 6:29037. DOI: 10.1038/srep29037.
  • In June 2016, MAISRC brought together a group of international experts to synthesize what is currently known about the ecology, impacts, and management of starry stonewort and identify key gaps in the science needed to better support management.

Current efforts

  • Assessing risk of further spread of starry stonewort in Minnesota
    • Using data on where starry stonewort has invaded in the U.S. to date to identify waterbody characteristics and environmental conditions associated with invasion risk
    • Identifying lakes in Minnesota in which starry stonewort may be more likely to survive and persist if introduced
  • Testing how long starry stonewort can remain viable out of water to assess risk of overland spread
  • Conducting laboratory experiments to test the efficacy and selectivity of different algaecides

Current projects

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