Glasswort is a name applied to various types of plants that were used to make soda-based glass in 16th century England, as opposed to potash or potassium carbonate based glass made from wood ashes. Many of these plants are also edible and are considered a delicacy in certain areas. Similar plants growing in the Mediterranean are often given the common name saltwort.
Though they come from a few different genera and do not form a biologically related group, glassworts share certain properties. They are succulent halophyte plants, meaning that they retain water and thrive in saline environments such as seashores and salt marshes. When burned, the ashes contain sodium carbonate, commonly called soda ash, an important ingredient in glass and soap. The great majority of glassworts are members of the amaranth family (Amaranthaceae), which also includes beets, spinach, and quinoa.
The name glasswort was first applied to plants of the Salicornia genus, including S. europea or common glasswort and S. bigelovii or dwarf glasswort, which is native to parts of the United States and Mexico. Parish's glasswort (Arthrocnemum subterminale), sometimes classified as a Salicornia species, is also native to California and Mexico. Many plants also belong to the Sarcocornia genus, such as beaded glasswort (S. quinqueflora), and thick-head glasswort (S. blackiana), both native to Australia. Some Sarcocornia species native to the United States are Pacific glasswort (S. pacifica) and Virginia glasswort (S. perennis).
Some glassworts native to Australia belong to the Tecticornia genus. Shrubby glasswort (Tecticornia arbuscula), like Parish's glasswort, was once classified as a Salicornia species. Salsola kali or prickly glasswort is one of the few glassworts native to Eurasia, and it has become an invasive species in North America and Australia. Glasswort buckwheat (Eriogonum salicornioides) belongs to a group of North American plants commonly known as wild buckwheat, and is the only glasswort that does not belong to the amaranth family.