Starry stonewort (Nitellopsis obtusa) can be found in slow moving rivers, lakes and ponds at depths of 3 to 95 ft. It prefers waters that are relatively high in calcium and phosphorus. In Vermont, starry stonewort is documented in Lake Memphremagog and Lake Derby.
Starry stonewort is a large, grass-like species of algae. It is light green throughout the growing season and has five to eight branchlets, or leaves, arranged in whorls around the stem. Both branchlets and stem are very thin. Starry stonewort is anchored by clear filaments called rhizoids. The rhizoids produce small, white, star-shaped bulbils (small bulblike structures), which are the easiest way to identify the plant.
Starry stonewort grows rapidly and forms dense mats that pose a threat to native vegetation. These mats can displace native plants and accumulate toxic substances known as phytotoxins that make the sediment inhospitable for other plant growth.
Starry stonewort also degrades fish spawning habitat and can impede their movement. If the mats reach the water surface, starry stonewort can interfere swimming, fishing, and boating as well.
Control and Prevention
Current treatment methods including manual and mechanical harvesting and herbicides have not been shown to have significant impacts on starry stonewort infestations. The best management option for starry stonewort is spread prevention.
Starry stonewort is spread in several ways, including by people through unintentional introductions, by water currents dispersing fragmented plant parts, and by animals to whose fur and feathers the star-shaped bulbils attach.
Prevent the spread of starry stonewort by practicing the Clean, Drain, Dry spread prevention methods. Drain all water from your boat, canoe, kayak, and other vessels and any equipment used in the water. Clean vessels and gear and remove all plant fragments and dispose of properly. Dry all damp areas of boats and vessels, such as livewells and bilges, with a towel and let air dry in the sun for at least five days before using in another waterbody. If this is not possible, rinse equipment with hot, high-pressure water.
VT Department of Environmental Conservation
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