Callitriche palustris aka Narrow Fruit Water Starwort

Callitriche palustris is a small water plant in the Plantaginaceae family. Common names include water starwort, water chickweed, and star grass. Its native range spans the temperate Northern Hemisphere to western Malesia. It is native to Britain and Ireland. Records also place it across much of Asia and North America. It grows at springs, in small streams, and along wet shores. Quiet water forms another part of its wild habitat.

The RHS describes an evergreen perennial that forms low mats. Kew instead lists it as an aquatic annual. These sources therefore differ on its life cycle. Plants reach about 0.33 feet [0.1 metres] in height. Their mats can spread widely over the water surface. The evidence gives no measured width for a mature plant. Leaves beneath the water are narrow and bright green. Those that float on the surface have broader blades. This change in leaf shape helps mark its aquatic form.

Small greenish-white flowers appear during summer. They draw little attention beside the green leaf mats. The plant suits shallow ponds and other quiet water features. The RHS also lists lakes, slow streams, and marshes as suitable settings. Its low form suits informal ponds and wildlife gardens. It can form a green cover across shallow water. The RHS gives a maturity period of two to five years.

Choose a sheltered site with constant moisture or submerged conditions. The RHS recommends sun or partial shade in its cultivation notes. Its position list also includes full shade. Loam is the listed soil type, with poor drainage suited to growth. Acid, neutral, and alkaline conditions all fall within its stated range. The RHS rates its UK hardiness as H5. This rating covers most UK sites, including those with severe winters. Divide plants to make more. Routine pruning is not needed, though spreading mats may need limits.

The RHS reports few usual pest or disease problems. Plants For A Future does not flag the species as weedy. That does not remove the need to watch its spread in small ponds. The same source lists leaves as edible after boiling and seasoning. It gives the plant a low food-use score of one out of five. It records no known hazards, but this is not proof of universal safety. It lists no known medicinal uses or other uses.