Starry Stonewort

Nitellopsis obtusa

Invader Images

    • Part of a starry stonewort plant
      Part of a starry stonewort plant
    • Underwater close-up view of starry stonewort
      Underwater close-up view of starry stonewort
    • Researcher holding a clump of starry stonewort attained through the ice on a Vermont lake
      Researcher holding a clump of starry stonewort attained through the ice on a Vermont lake
    • View of the star-shaped bulbil that gives the plant its name
      View of the star-shaped bulbil that gives the plant its name
    • Clump of starry stonewort
      Clump of starry stonewort
    • Starry stonewort viewed underwater
      Starry stonewort viewed underwater


Nitellopsis obtusa is a grass-like macroalgae that is most easily identified by its white, 2-5 mm star shaped bulbils that are produced on clear threads called rhizoids. These bulbils can be found over the entire plant and throughout the year. However, if the bulbils are not present, N. obtusa can also be identified by its uneven forking pattern, which is caused by the growth of short bracts from the branchlets. Common look-a-likes have branchlets that fork evenly. Branchlets are arranged in whorls of 5-8 with a larger internodal space than most other plants. Most stem and branchlets are around 1 mm in diameter and the stem is smooth to the touch.



Starry Stonewort is native to the west coast of Europe all the way to Japan.


Nitellopsis obtusa is typically found in slow moving shallow waters, but can also be found at deeper depths (8 m), often near docks and marinas. This species prefers waters that are relatively high in calcium and phosphorus.


N. obtusa in its native range is an annual alga that dies off during the colder months of winter, sometimes persisting through milder winters. However, in Michigan, N. obtusa has been observed to persist throughout the winter, only to die off during early spring. This species is dioecious and can reproduce sexually via its orange oospores, as well as asexually via the star-shaped bulbils. The oospores are thought to be a mode of dispersion as they can easily attach to the feathers or fur of animals.

Ecological Threat

Nitellopsis obtusa is able to grow rapidly and form dense mats that can cause a variety of problems. These dense monospecific mats can block suitable fish spawning habitat and crowd out native plant species. If the mats reach the water’s surface, they can also hinder recreational use of the water body. Thick N. obtusa mats often act as benthic barriers and accumulate phytotoxins and make sediments inhospitable for plant growth.

Management Options

Legal Status

It is illegal to transport any aquatic plant under the Vermont nuisance species transportation law.

Control Options & Examples

Current management of starry stonewort in Vermont is focused on spread prevention. Decontamination of boats, trailers, and any gear that may have been in the infested water body is strongly encouraged in order to stop the spread of invasive species. Draining all water from motors, live wells, and bilges and letting them dry before the next use is good practice that can also reduce the spread of invasive species. Chemical treatment with herbicides or algaecides has been tried elsewhere in the past, but due to the high density mats N. obtusa can form, these treatments often only reach the mat’s upper levels, allowing the deeper portions to continue growing.

Vermont Distribution

Starry stonewort is currently found in Lake Memphremagog and Lake Derby, Vermont. Elsewhere, it is found in the Great Lakes and surrounding waterbodies.

Starry stonewort distribution map

How You Can Help

For most aquatic invasive species, humans are the primary vector of transport from one waterbody to another. Many of these nuisance plants and animals can be unknowingly carried on fishing gear, boating equipment, or in very small amounts of water in a watercraft. The easiest and most effective means to ensure that you are not moving aquatic invasives is to make sure that your vessel, as well as all your gear, is drainedclean, and dry.


  • CLEAN off any mud, plants, and animals from boat, trailer, motor and other equipment. Discard removed material in a trash receptacle or on high, dry ground where there is no danger of them washing into any water body.

  • DRAIN all water from boat, boat engine, and other equipment away from the water.

  • DRY anything that comes into contact with the water.  Drying boat, trailer, and equipment in the sun for at least five days is recommended. If this is not possible, then rinse your boat, trailer parts, and other equipment with hot, high-pressure water.

Interested in monitoring for aquatic invasives?


Bharathan S (1987) Bublils of some charophytes. Proceedings of the Indian Academy of Sciences 97:257–263.

Crawford G (2011) A new invasive in our midst: the starry stonewort saga. In: Michigan Inland Lakes Conference. Boyne Falls, MI, pp 1–44

Hackett RA, Caron JJ, and Monfils AK (2014) Status and Strategy for Starry Stonewort (Nitellopsis obtusa (N.A.Desvaux) J.Groves) Management. Michigan Department of Environmental Quality, Lansing, Michigan.

Kipp, R.M., M. McCarthy, A. Fusaro, and I.A. Pfingsten. 2016. Nitellopsis obtusa. USGS Nonindigenous Aquatic Species Database, Gainesville, FL. Revision Date: 6/21/2016 

Mills, E.L., J.H. Leach, J.T. Carlton, and C.L. Secor. 1993. Exotic species in the Great Lakes: a history of biotic crises and anthropogenic introductions. Journal of Great Lakes Research 19(1): 1-54.

Pullman GD, Crawford G (2010) A decade of starry stonewort in Michigan. Lakeline 36–42.

Soulie-Marsche, I., M. Benammi, and P. Gemayel. 2002. Biogeography of living and fossil Nitellopsis (Charophyta) in relationship to new finds from Morocco. Journal of Biogeography 29(12): 1703-1711.