Distribution
See also: Carnivorous plants of AustraliaThe range of the sundew genus stretches from Alaska in the north to New Zealand in the south. The centers of diversity are Australia, with roughly 50% of all known species, and South America and southern Africa, each with more than 20 species. A few species are also found in large parts of Eurasia and North America. These areas, however, can be considered to form the outskirts of the generic range, as the ranges of sundews do not typically approach temperate or Arctic areas. Contrary to previous supposition, the evolutionary speciation of this genus is no longer thought to have occurred with the breakup of Gondwana through continental drift. Rather, speciation is now thought to have occurred as a result of a subsequent wide dispersal of its range. The origins of the genus are thought to have been in Africa or Australia.
Europe is home to only three species: D. intermedia, D. anglica, and D. rotundifolia. Where the ranges of the two latter species overlap, they sometimes hybridize to form the sterile D. × obovata. In addition to the three species and the hybrid native to Europe, North America is also home to four additional species; D. brevifolia is a small annual native to coastal states from Texas to Virginia, while D. capillaris, a slightly larger plant with a similar range, is also found in areas of the Caribbean. The third species, D. linearis, is native to the northern United States and southern Canada. D. filiformis has two subspecies native to the East Coast of North America, the Gulf Coast, and the Florida panhandle.
This genus is often described as cosmopolitan, meaning it has worldwide distribution. The botanist Ludwig Diels, author of the only monograph of the family to date, called this description an "arrant misjudgment of this genus' highly unusual distributional circumstances (arge Verkennung ihrer höchst eigentümlichen Verbreitungsverhältnisse)", while admitting sundew species do "occupy a significant part of the Earth's surface (einen beträchtlichen Teil der Erdoberfläche besetzt)". He particularly pointed to the absence of Drosera species from almost all arid climate zones, countless rainforests, the American Pacific Coast, Polynesia, the Mediterranean region, and North Africa, as well as the scarcity of species diversity in temperate zones, such as Europe and North America.
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