Nitellopsis obtusa

Nitellopsis obtusa is a large freshwater alga. It is also known by the common name starry stonewort. This alga grows to a length of over 1.5 m, is bright translucent green and has branches growing in whorls from the main axis the plants easily break up. It is easily distinguished from other charophytes by star-shaped bulbils which permit vegetative reproduction.

Description
Nitellopsis 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 in diameter, and the internodal lengths of stem consist of a single cell which may be several centimetres long. Stems may be up to 80 cm or even longer and form dense masses. When in active growth, the colour is light green. At the base of the main stems, there may be creamy-white bulbils. The rhizoids are star-shaped. 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.

Habitat
This alga grows in freshwater to a depth of over 4 m, 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, typically near docks and marinas.

Distribution
Nitellopsis obtusa is widely dispersed in Europe and Asia. It is known from only a few sites in the British Isles, and these include Cosmeston Lake in the Vale of Glamorgan. It has invaded the Laurentian Great Lakes in North America.