Charophytes, also known as stoneworts, are a group of large, multicelluar green algae that live in a variety of freshwater and brackish habitats. Charophytes play a significant role in aquatic ecosystems as early colonisers and habitat providers for a variety of organisms. They can be indicators of good water quality and different species have different environmental requirements (e.g. temperature, salinity). The presence of a species can be used to infer ecological characteristics of water bodies and habitats.

The Natural History Museum, London, holds a collection of >20,000 specimens of charophytes, among which there are approximately 5,000 from UK and Ireland. The majority of specimens were collected between c.1890 and c.1920 (during the hey-day of amateur botanical collecting and botanical clubs), although there are significant earlier records and many later specimens of different species. The collection includes herbarium sheet, fluid-preserved, microscope slides and oospore material. It is a comprehensive collection, including all the species and varieties that have been collected in the UK and Ireland.

This dataset provides a complete catalogue of all the British and Irish herbarium sheet material in the Charophyte collection. For each specimen details of the identification, collector, date and mapped locality are provided. Many of these specimens have images associated with them, such as a photograph of the herbarium sheet or Scanning Electron Microscope images of the oospores.