Starry Stonewort

Nitellopsis obtusa

Photo: Creative Commons Lorenz Seebauer. Photo: Creative Commons Kristian Peters. Drawing: Douglas Pullman, Gary Crawford. 2010.

Description

Nitellopsis obtusa is a bushy, bright green macro-algae that produces a characteristic star-shaped bulbil. N. obtusa has long, fairly straight branches arranged in whorls, attached at nodes to the stem at an acute angle. Both stem and branches are about 1 mm (0.04 in) in diameter, and the internodal lengths of stem consist of a single cell which may be several cm long and breaks apart easily. Stems may be up to 80 cm (31 in) or even longer and form dense masses. Plants are either male or female. The oogonia (female reproductive structures) form at the base of upper branchlets and orange to red oocytes can occur, which help distinguish this alga from the rather similar musk-grass and brittlewort.

General Information

N. obtusa grows in freshwater to a depth of over 4 m (13 ft), on soft substrates such as silt, sand and accumulations of detritus. It tends to grow in deep, slow moving water where other plants are scarce. N. obtusa is native to Europe and Asia and was unintentionally introduced into the United States’ Great Lakes through the discharge of contaminated cargo ship ballast water. The first known occurrence in the United States was in 1978 along the St. Lawrence River.