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Hydrilla

Starry Stonewort (Nitellopsis obtusa)

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

Overview

Regulated areas of hydrilla
Nitellopsis obtusa is prohibited (Red counties)

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:

  • Invades lakes, rivers, reservoirs and ponds. Can grow in water depths up to 9 meters.
  • It can reduce fish spawning habitats, outcompete other vegetation, and fragments can foul watercraft motors.

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 developed by the department.

Identification

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.

Starry Stonewort

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 to this species.

Distribution

Nitellopsis obtusa
Counties in WI where starry stonewort has been reported. Both vouchered and unvouchered reports included.

Do you have starry stonewort in your county but it isn't shaded on the map? Have you seen it? Send us a report.

Control

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 waterbodies, and to educate the public about presence if it is found.

Photos

View Starry stonewort pictures in our photo gallery!

Resources


Links for More Information

Last revised: Monday August 24 2015