Nitellopsis obtusa (Desvaux in Loiseleur) J. Groves, (1919)

Common Name: Starry stonewort

Synonyms and Other Names:

Chara obtusa, C. ulvoides, C. stelligera, Lychnothamnus stelliger, Nitella stelligera, N. stelligera var. ulvoides, N. ulvoides, N. bertolonii, Nitellopsis aculeolata, N. obtusa var. ulvoides, N. obtusa f. ulvoides , Nitellopsis stelligera, Tolypellopsis obtusa, T. stelligera, T. ulvoides

Jim Grazio, PA DEP 2015Copyright Info


Stem/Rhizoids: Nitellopsis obtusa has long, variable-length, relatively straight branches arranged in whorls that attach at acute angles to stem nodes. Internodal cells of N. obtusa are quite large, often on the order of a few centimeters long (Steudle and Zimmermann 1977, Yoshioka and Takenaka 1979). Most stem and branch cells are around 1 mm in diameter, while stems can reach up to 80 cm long (Hargeby 1990, Sher-Kaul et al. 1995). Heights of 2 m have been observed at a depth of 9 m in one Michigan lake (Pullman and Crawford 2010), although rate of growth is uncertain. N. obtusa is light green when actively growing. Creamy white bulbils may occur at the base of the main axis just below the substrate-water interface and on branches of the main axis at nodes; rhizoids are star-shaped.

Reproductive structures: Plants are dioecious. Female oogonia, with bracts on either side, form at the upper nodes of branchlets. Plants can form gyrogonites, which are calcified, spiral-shaped fructifications (Bharathan 1983, 1987, Schloesser et al. 1986, Soulie-Marsche et al. 2002). Orange to red oocytes can occur at the nodes of branches (Pullman and Crawford 2010).

Look-a-likes: Chara spp. musk-grass; Nitella spp. brittlewort; other Nitellopsis spp. stonewort. Key differences are the star-shaped rhizoid, the orange-colored oocyte, irregular branching, and lack of a garlic odor (Pullman and Crawford 2010).

Size: Up to 2 m in height (Pullman and Crawford 2010); main stem up to 80 cm long (Hargeby 1990).

Native Range: Nitellopsis obtusa is native to Eurasia, from the west coast of Europe to Japan (Mills et al. 1993, Soulie-Marsche et al. 2002).

Nonindigenous Occurrences: First U.S. occurrence was in 1978 along the St. Lawrence River (Geis et al. 1981; Mills et al. 1993). Present range includes much of the Great Lakes Region, and parts of the Upper Mississippi-Crow-Rum Basin, the Rock Basin, the Upper Illinois Basin, the Allegheny Basin, the Upper Susquehanna Basin, and the St. Francois River Basin:

  • Indiana - Initially discovered in 2008 at Lake Wawasee near Syracuse (Edgell 2011; Aquatic Weed Control 2015). Currently in 8 lakes in northeastern Indiana (Edgell 2011; Pearson 2015; Aquatic Enhancement & Survey, Inc. 2015).
  • Michigan - First found in 1983 at Lake St. Clair, along the St. Clair and Detroit Rivers (Schloesser et al. 1986). Now occurs at lakes in all Lower Peninsula basins and in Millecoquins Lake of the Upper Peninsula (Pullman and Crawford 2010; Michigan State University 2015; Bagley 2015). Michigan has the most reported occurrences of any state.
  • Minnesota - Only two known occurrences, both in 2015 at Mud Lake and Lake Koronis (MN DNR 2015).
  • New York - First spotted in 1978 along the St. Lawrence River (Geis et al. 1981; Mills et al. 1993), and later in 1981 at Lake Ontario (iMapInvasives 2015). Since 2005, starry stonewort was found at Oneida, Chautauqua, Otisco, Otsego, and Cayuga Lakes (iMapInvasives 2015).
  • Pennsylvania - Only occurrence was at Presque Isle Bay near Erie; first seen in 2009 (EnviroScience, Inc. pers. comm. 2009) and confirmed in 2012 (Jim Grazio, PA DEP pers. comm. 2015).
  • Vermont - Discovered in 2015 in a small cove at southeastern Lake Memphremagog (FLOW 2015).
  • Wisconsin - Found in 2014 at Little Muskego Lake (WI DNR 2014). Additional starry stonewort was spotted in 2015 at Silver, Long, Pike, Big Muskego, and Bass Bay Lakes (WI DNR 2015).

Ecology: Nitellopsis obtusa is sometimes found in deep, slow moving water where other plants are scarce, typically near docks and marinas (Midwood et al. 2016). Nitellopsis obtusa is known to maintain permanent populations in freshwater or brackish water with salinity up to 5%. It can tolerate salinity fluctuations up to 17% for around 1 week. Under high salt loading or unfavorable environmental conditions, it has the ability to shift cells from a high-energy state to a state of passive permeability. It experiences suppressed growth at water temperatures of 30°C. In such conditions, apical cells no longer form and some plant cells may die (Marchyulenene et al. 1982, Moteyunene and Vorob’ev 1981, Winter et al. 1999). In areas of dense vegetation, N. obtusa forms “pillows” of various heights; as growth slows, these pillowed mats may develop circular clearings (Pullman and Crawford 2010). Under eutrophic conditions, it often produces oospores (Bharathan 1987).

Nitellopsis obtusa occurs at depths of 1–3.5 m in relatively protected zones of the St. Clair-Detroit River system at water velocities of 3–11 cm/s; on soft substrates such as silt, sand, and fine detritus; and where light transmittance ranges from 1–50%. In this system, it first appears around July and reaches highest biomass levels in September, gradually declining until March of the following year, when it decomposes. It has been recorded in water temperatures of 0–24°C in this area. It occurs more in the Detroit River than the St. Clair River, while other stoneworts (Family Characeae) occur more frequently in the latter. The environmental parameters determining stonewort distribution in these two rivers are not known. In the St. Lawrence River, it is uncommon in early July but increases through September. It occurs at an average depth of 4.8 m depth and 6% light transmittance. In its native habitat, it is typically found at depths of 3–8 m, preferring deeper habitats with low light transmittance but relatively high calcium and phosphorus content, where other stoneworts generally occur less frequently (Berger and Schagerl 2004, Nicholls et al. 1988, Schloesser et al. 1986).

Means of Introduction: Nitellopsis obtusa was very likely introduced in ballast water to the Great Lakes (Mills et al. 1993, Schloesser et al. 1986). Nitellopsis obtusa produces oocytes that can easily become attached to the fur and feathers of mammals and birds that inhabit infested areas. This mechanism is an efficient way for N. obtusa to spread rapidly amongst inland lakes (Pullman and Crawford 2010). The alga also spreads via fragmentation (Pullman and Crawford 2010).

Status: Established in Indiana, Michigan, Minnesota, New York, Pennsylvania, Vermont, and Wisconsin.

Great Lakes Impacts:

Nitellopsis obtusa has a moderate environmental impact in the Great Lakes.

When it was first reported, N. obtusa was the ninth most frequently collected macrophyte in the St. Clair-Detroit River system (Mills et al. 1993, Nicholls et al. 1988). It was recorded at a peak biomass of 259 g m-2 in September, when many other macrophytes were declining, giving it a competitive advantage (Nicholls et al. 1988, Schloesser et al. 1986). Once established in inland lakes, N. obtusa forms dense mats of vegetation that completely cover the lake bottom. Mats of N. obtusa can act like a commercial benthic barrier and lead to the accumulation of phytotoxins that could create redox conditions; these conditions have a reduced impact on the rootless N. obtusa as compared to native species (Pullman and Crawford 2010).

Mats of N. obtusa also correspond with a dramatic decrease in the biomass of competing species. Although specific surveys have not been conducted yet, there is serious concern for inland lake populations of native species that are dependent on lake bottom habitat, including minnows, logperch, darters, clams, and other invertebrates (Pullman and Crawford 2010). Dense mats of N. obtusa directly impact the habitat used by native fish for spawning. Bass and sunfish are known to regularly spawn in dense growths of native Chara species, but these spawning behaviors did not occur in correspondingly dense growths of N. obtusa (Pullman and Crawford 2010).

Nitellopsis obtusa has been associated with increased water clarity in inland lakes, which could in part be due to their association with zebra mussels (Dreissena polymorpha) as a favored substrate. In spite of increased water clarity from the mussels, the dense growth of N. obtusa actually reduces light availability for other submersed flora (Pullman and Crawford 2010).

There is also research indicating that macrophyte species have a strong influence on phytoplankton through allelopathic interactions (Hilt et al. 2010, Mulderij et al. 2007, Pullman and Crawford 2010). In Sweden, N. obtusa dies off in the winter, which reduces the ability of slow colonizers like the isopod Asellus and amphipod Gammarus to establish significant populations in this habitat. As a result, it typically hosts many chironomids, while Chara tomentosa harbors more amphipods and isopods (Hargeby 1990).
In Lake Majcz Wielki, Poland, zebra mussels settle at densities of 1000 per m2 on N. obtusa and Stratiotes aloides, and at much lower densities on other plants (Lewandowski and Ozimek 1997).

There is no indication that N. obtusa is affecting Great Lakes native populations genetically, but it has been proposed that the population of N. obtusa in the Great Lakes represents a unique phenotype from its native population in Europe (Pullman and Crawford 2010).

Nitellopsis obtusa has a high socio-economic impact in the Great Lakes.
There is a large economic investment from inland lake communities to manage and control invasions of N. obtusa. This is both to protect boat owners from potential damage to their vessels, as well as to maintain economically important recreational fishing and swimming areas (Pullman and Crawford 2010). Moreover, N. obtusa poses a risk of entanglement to swimmers, who also are displeased with this alga’s rough texture (R. Sturtevant , pers. comm.).

As one of the filamentous algae that frequently detaches from the bottom to form a floating mat, N. obtusa contributes both to lake “scum” and mats that wash up on beaches (R. Sturtevant, pers. comm.).

While N. obtusa negatively affects water quality for other macrophyte and phytoplankton species, there is no evidence to suggest that the quality of drinking water is significantly affected. However, there have been no studies conducted to specifically address this issue.

Nitellopsis obtusa is a relatively new invasion, particularly to the inland lakes. The long term impacts on the economic value lake property cannot yet be properly assessed.

There is little or no evidence to support that Nitellopsis obtusa has significant beneficial effects in the Great Lakes.
Nitellopsis obtusa is becoming regarded as the most aggressive invasive species in inland lakes and has been recorded replacing other nonnative and nuisance species, including Eurasian watermilfoil (Myriophyllum spicatum), fanwort (Cabomba caroliniana), and curly leaf pond weed (Potamogeton crispus) (Pullman and Crawford 2010). Hilt et al. (2010) suggested that N. obtusa could be an effective means of restoration for deep lakes in its native range.

Nitellopsis obtusa has a significant stratigraphical account that extends back to the early Quaternary and can be useful in biogeographical research, and well as in tracing evolutionary lineages (Soulie-Marsche et al. 2002).

In European regions, this species can be a good substrate for epiphytes, even though it is frequently covered in marl, which is a byproduct of photosynthesis formed when bicarbonate is used (Brindow 1987). It is known to have allelopathic properties towards cyanobacteria (Berger and Schagerl 2004). Nitellopsis obtusa increases in the Netherlands have been associated with increases in populations of red-crested pochards (Netta rufina), which feed preferentially on this species, possibly because it is a good source of calcium and sulfur (Ruiters et al. 1994).

Management: Regulations (pertaining to the Great Lake region)

There are no known regulations for this species.

Note: Check federal, state/provincial, and local regulations for the most up-to-date information.

There are no known biological control methods for this species

It is difficult to mechanically remove all of a N. obtusa population from an inland lake because of the large amounts of biomass. Additionally, even when entire plants are removed, N. obtusa is typically the first macrophyte to reestablish the disturbed area because it is such an aggressive and efficient recolonizer (Pullman and Crawford 2010).

Nitellopsis obtusa is very sensitive to common algaecides containing copper and endothall based compounds. When N. obtusa is still low growing, algaecide treatment can treat the entire organism. However, in taller individuals, the algaecide is absorbed in the top of the plant, killing that portion but leaving the bottom of the plant alive. This type of treatment has been found to be somewhat successful and is called a “hair cut treatment” by managers. The timing of the algaecide treatment is also important. Treatment early in the spring could help open up spawning habitat for native fish species, but N. obtusa or other nonnative aquatic plants are likely to recolonize these areas in the early summer (Pullman and Crawford 2010).

Note: Check state/provincial and local regulations for the most up-to-date information regarding permits for control methods. Follow all label instructions.

Remarks: Nitellopsis obtusa was thought to have been locally extirpated in some regions of its native range where it has been rediscovered—for example, in parts of Germany (Golombek 1998, Raabe 2006) and Japan (Kato et al. 2005). It is considered rare in Bremen, Germany but has recently increased in abundance in some lakes (Trapp and Kirst 1999). Populations are considered somewhat vulnerable in Sweden (Blindow 1994).

References: (click for full references)

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Author: Kipp, R.M., M. McCarthy, A. Fusaro, and I.A. Pfingsten

Contributing Agencies:

Revision Date: 6/21/2016

Citation for this information:
Kipp, R.M., M. McCarthy, A. Fusaro, and I.A. Pfingsten, 2017, Nitellopsis obtusa (Desvaux in Loiseleur) J. Groves, (1919): U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL, and NOAA Great Lakes Aquatic Nonindigenous Species Information System, Ann Arbor, MI,, Revision Date: 6/21/2016, Access Date: 10/23/2017

This information is preliminary or provisional and is subject to revision. It is being provided to meet the need for timely best science. The information has not received final approval by the U.S. Geological Survey (USGS) and is provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the information.