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Starry Stonewort

(Nitellopsis obtusa)

Photo of starry stonewort
Photo credit: Paul Skawinski

Starry stonewort, a submerged annual macroalga belonging to the order Charales (includes all Chara and Stonewort species), is known to cause nuisance conditions in Michigan, New York and Indiana. It can outcompete other vegetation and form monotypic stands that can reduce fish spawning habitat.

 Overview map of prohibited classification in WI
Prohibited (red) counties

Classification in Wisconsin: Prohibited

Other names for this macroalga include:

  • Common names: green alga
  • Scientific names: Nitellopsis obtusa
  • Former names: Chara obtusa, Nitellopsis stelligera, Tolypellopsis obtusa, T. stelligera
Ecological Threat
  • It invades lakes, rivers, reservoirs and ponds. It can grow in water depths up to 9 meters.
  • It can reduce fish spawning habitats, outcompete other vegetation and fragments can foul watercraft motors.

Leaves: Whorls of 4-6 branchlets (leaves) with blunt tips and irregular-length branchlets are arranged along the primary thallus (stem).

Fruits & seeds: Only male individuals in North America have been documented and reproduction is via fragments or vegetative structures called "bulbils, " the primary identifying characteristic. Bulbils are produced at nodes and most are found on the rhizoids. These bulbils are 3-6 mm wide and star-shaped with five or more points (see image below). The male specimen may produce orange–to–brown colored antheridia in branchlet axils.

Photo of starry stonewort bulbil
Photo credit: Paul Skawinski

Roots: Clear rhizoids

Similar species: Similar characteristics to other charophytes like Nitella and Chara species and may be difficult to distinguish from starry stonewort. Star-shaped bulbils are a unique feature of this species.


See the reported locations of starry stonewort in Wisconsin.

Do you know of additional populations? Please send us a report.


Current control methods have not been shown to have a measurable impact on starry stonewort. Special care should be taken to reduce the spread of starry stonewort within and amongst water bodies and to educate the public about its presence if it is found.

Sources for content: Starry Stonewort Management - Department Factsheets: Links for more information: