Skip to main content

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 forms monotypic stands that can reduce fish spawning habitat.


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

Classification in Wisconsin: Prohibited

Species Assessment Groups (SAG) were assembled to recommend a legal classification for each species considered for NR 40. The recommendation for starry stonewort was based upon this literature review [PDF] developed by the department.


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

Fruits & seeds: Only male individuals in North America have been documented and reproduction is via fragments or vegetative structures called "bulbils" which is the main identifying characteristic. Bulbils are produced at nodes and most are found on the rhizoids. These bulbils are 3-6 mm wide, star-shaped with 5 or more points (see image below). 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? 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 presence if it is found.


View starry stonewort pictures in our photo gallery!


Sources for content: Links for more information: