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Botanists created the name callitriche by combining the Greek word calos, meaning beautiful, with the Greek word for hair, trichos. The beautiful, thin stems of the aquatic plant inspired this name. It is a genus of the Plantaginaceae family, but it used to belong to the Callitrichaceae family. It is found in almost all regions of the world that have shallow water or wetlands. The common name for these plants is starwort.
Botanists debate whether callitriche plants are native to places such as the New World and Australia or if they were introduced or naturalized. There are approximately 25 species of callitriche plants worldwide, and about 22 of those are present in regions in the New World. About nine species are native to the British Isles. The species Callitriche stagnalis is native to the African countries of Tunisia, Algeria, and Morocco, as well as most of Europe and Asia. Some species are endemic to only one region, like the C. marginata or California water starwort, which is found only in California.
Amateur botanists have difficulty categorizing most of these plants. Often the only noticeable difference is in the fruit, and typically botanists use a magnification of 10 to 20 times to analyze the fruit before classifying the plant. To the untrained eye, some starworts resemble other water plants, such as the common duckweed, which is often an invasive species. Another problem with identifying the individual species is the plant's tendency to exhibit different features in different growing conditions.
Most of the plants have two different types of leaves: floating and submerged. In most species, the submerged leaves grow in pairs along the stems and vary in size from less than 0.25 inches (about 0.5 cm) to 1 inch (about 2.5 cm). Often the floating leaves are less than 0.5 inches (1.0 cm) wide and may be oval or roundish in shape. In the C. verna, the submerged leaves are linear or ribbon-like, and the C. stagnalis and related species have elliptical-shaped submerged leaves. C. hermaphroditica, or northern water starwort, has a linear leaf shape, and the leaves are wholly submerged with no floating leaves.
The flowers of the callitriche plants tend to be very small and bear no petals or sepals, which are petal-like flower parts. These plants often have white bracts that grow at the leaf base. Many of the species have unisexual flowers and are self-pollinating. Each flower may produce up to four tiny fruits that are often heart-shaped or have two ovals joined. Each fruit produces only one seed.
Callitriche plants grow in shallow waterways or wetlands where the plants can draw nutrients from the mud. The roots generally are loosely anchored, and the plant is easily dislodged. This fragility is one of the reasons that many species are endangered in their native regions. For example, in 2011, the Wisconsin Department of Natural Resources listed the large water starwort, or C. heterophylla, as threatened in Wisconsin and Michigan.
Generally, callitriche plants are not a valuable crop plant. Some herbalists use the plant as a diuretic, but generally no scientific study has endorsed its healing qualities. Other uses include livestock grazing. In Australia, the C. cyclocarpa, or western water starwort, is on the vulnerable list because domestic livestock, feral rabbits, and feral pigs have eaten a large amount of the plants.