to a factsheet about starry stonewort

Learn the facts about starry stonewort
Starry stonewort (Nitelliposis obtusa) is an invasive green alga that has spread rapidly within some
northern-tier lakes. It can grow tall and dense, forming mats on the surface that interfere with recreation
and potentially displacing native plant species. Starry stonewort is a charophyte, a group that also
includes muskgrasses and stoneworts (Chara and Nitella species) that are native to Minnesota. It is
native to parts of Europe and Asia but is relatively uncommon in much of its native range and is
considered endangered in Japan and of conservation concern in Britain.
What it looks like
What it affects
Starry stonewort can look quite similar to some native
Where starry stonewort grows densely and forms surface
charophytes, but may appear larger and more robust. It is a
mats, it can interfere with boating and other recreational
green macroalga with whorls of long, narrow branchlets in
activities. Dense growth may also displace native plants and
groups of 4 to 6 coming off of main shoots. Orange
could potentially have impacts on fish and other animals.
reproductive structures (male antheridia) occur at branchlet
Starry stonewort’s ecological impacts are not well
nodes. Small, white, star-shaped bulbils are a distinguishing
understood, and there has been little published research
feature that gives it the name starry stonewort.
to date.
Life cycle
How it spreads
Starry stonewort is dioecious, meaning that individuals are
either male or female — unlike many plants and algae that
have both male and female reproductive parts. Interestingly,
the best evidence to date indicates that the populations in
the U.S. are all male, though there may be undiscovered
females. This means that spread of starry stonewort is
probably through human movement of fragments from lake
to lake. In particular, starry stonewort produces small,
star-shaped structures called “bulbils” that allow it to
reproduce vegetatively (clonally).
Starry stonewort appears to be spreading vegetatively in the
U.S. (by bulbils and fragments). Accidental movement by
people is the most likely means of dispersal. Many of the
known infestations occur in high-use waterbodies and near
boat accesses.
Where it’s found
Starry stonewort was first found in North America in 1978 in
the St. Lawrence River and has spread inland since. It is now
found in much of Michigan’s Lower Peninsula and many
locations in New York State. It has also been found in
Indiana and was discovered in southeastern Wisconsin in
2014. It was first recorded in Minnesota in 2015 (Lake
Koronis, Stearns Co.).
Photos: MyMuskegonNow.com; Paul Skawinski; Jason Wachter; MN DNR
Starry stonewort research at the
Minnesota Aquatic Invasive Species Research Center
There is a high level of uncertainty about the future of starry stonewort and its potential impacts in Minnesota, as well as
uncertainty about how to best control this species where it has invaded. Researchers at the Minnesota Aquatic Invasive Species
Research Center are currently performing ecological niche modeling to assess starry stonewort’s risk of spread throughout the state.
This involves using data on where starry stonewort occurs in its native and invaded ranges — and environmental and climatic data
associated with those occurrences — to predict areas of suitable habitat where it could potentially invade and persist if introduced.
Through this work, we have learned that starry stonewort appears to be occupying a climate niche in its invaded range different
from where it occurs in its native range.
Future research will involve further assessing spread risk and evaluating options for starry stonewort control. We will perform
finer-scale risk assessment for Minnesota lakes, desiccation trials to test risk of movement to new lakes through contaminated
boats, and growth experiments to evaluate starry stonewort’s performance under different climate scenarios for Minnesota.
To improve the toolkit for starry stonewort control, we will test sensitivity of starry stonewort to different herbicides, while also
evaluating non-target effects on native charophytes and vascular plants.
MAISRC is also bringing together a group of international
experts to synthesize what is currently known about the ecology,
For more information:
impacts, and management of starry stonewort and identify key
Visit: www.maisrc.umn.edu/starry-stonewort
gaps in the science needed to better support management.
Contact: Dr. Daniel Larkin
Assistant Professor & Extension Specialist
[email protected]
www.maisrc.umn.edu
Funding for MAISRC is provided by the Environment and Natural Resources Trust Fund, the Clean Water Fund, and private donations.