Common Club-rush

Schoenoplectus lacustris grows up to 3.5 metres (11 ft) tall, with mid to dark green (not glaucous) stems 5–15 mm (0.2–0.6 in) thick. Most of the leaves of S. lacustris are reduced to bladeless sheaths around the stem, but leaf blades up to 100 cm (40 in) long can be formed under water. The inflorescence appears at the top of the stem, and comprises 3–10 branches, each of which is up to 10 cm (4 in) long and may be again divided into shorter branches. The flowers are in the form of spikelets, each of which is 6–15 mm (0.2–0.6 in) long by 3–5 millimetres (0.1–0.2 in) wide. It typically grows in water 0.3–⁠1.5 m deep, but can grow in water deeper than this. The stems are round in cross-section, in contrast to the triquetrous (rounded-triangular) stems of other species in the genus, such as S. triqueter and S. pungens. The stems of S. tabernaemontani (grey club-rush) are also round, but S. tabernaemontani is a smaller plant, less than 1.5 m (5 ft) tall, with only two stigmas per flower, and has glaucous grey-green stems.

Schoenoplectus lacustris is widespread in Europe, albeit rare in the far north, and extends eastwards into Asia as far as Mongolia. It is also found in a number of Mediterranean sites in North Africa, and has been introduced to Bangladesh and Haiti.