Drosera: The Sundews
Currently vying with the bladderworts for the position of largest genus of carnivorous plants, the sundews are a broad, ubiquitous group spanning every continent (save for Antarctica of course) and nearly every habitat type except for true desert regions. From the tropic rainforests of northern Australia and the Amazon, to highland bogs and seeps of mountain ranges and even the peatlands of the Tundra, there is a species for nearly every region imaginable (and for those in the US, sundews can be found in almost every single state). Sundews range immensely in size too, from the tiny half-inch pygmies of Australia to the King and Magnificent Sundews of South Africa and Brazil, or the massive branching and climbing stems of some tuberous Australian species.
The vast size of this genus provides a lot of room for diversity and distinct groups among species, with many sundews being so far removed from each other that they are barely reminiscent of each other (save for having sticky traps) and even at one point divided into several different genera of their own. The species accounts below are arranged into either distinct groups of related species, or by regions containing large numbers of unique species. These include the tuberous sundews, pygmy sundews, Latin American and South African groups, among others.
Sundews possess a long history, being among the first carnivorous plants described by people (a manuscript dating back to the 1400's with a distinct picture of a sundew in it is still yet untranslated), and were among the plants used by none other than Charles Darwin himself to prove that plants could eat animals. So enamored was Darwin with the properties of these strange, sticky plants that could move on their own that he once quoted, "I care more about the history of Drosera than that of the origin of all the species on earth." From the father of the theory of evolution, that's quite a claim. Many sundews are also purported to have medicinal properties, the secretions of the glands as well as extract of leaves of such species as D. anglica and D. rotundifolia used as anti-inflammatory medications (though in some cases they have also been adopted in homeopathic medicines, leaving many skeptical of their true attributes).
Many people are also surprised to learn that sundews are the closest relatives to such different looking plants as the Venus Flytrap and Waterwheel plant, the only snap-trap carnivores known. One look at plants such as D. falconeri however might show how plants with sticky moving leaves might have turned instead into snapping jaws. An even more ancient ancestry might be shared with several other carnivorous groups as well, including the Dewy Pine, African Hookleaf, and the tropical pitcher plants.
Once considered to all be a single, highly variable species, this group of Australian-Asian sundews (subgenus Drosera, section Arachnopus) are united by tall stems and filiform leaves, annual growth habits, and a menagerie of unusual glands on the stems and leaves. Some taxa are still being fleshed out, particularly the nominal species which still includes all plants found across most of southern to western Asia and plants reported from Africa.
Latin American Species
Section Brasiliae, many species of the "capillaris complex," and unusual mountainous and southern-temperate species comprise this vast and variable group.
Tropical African Sundews
Africa and Madagascar are home to a unique group of sundews, many of them stem-forming oddities or plants reminiscent of the South American "capillaris group" (possibly possessing a common ancestor?). Some species span more than the tropics, also extending into another unique domain: South Africa. Those species endemic to the southern tip of Africa have another section below however.
Across many parts of the world are species that don't quite fit into any other larger groups: the spatulata complex, many unique and solitary Australian species, the Queensland Sisters, etc. If it doesn't land in the other categories, you'll find it here.
Northern Temperate Sundews
Though this group consists mostly of those species that are primarily distributed across the vast temperate regions of the northern hemisphere, a few of these species also have unique extensions into the tropics, or are unusual exceptions to otherwise tropical groups. Some of these species have the greatest distributions of any sundew, extending across multiple continents for circumboreal ranges.
The Petiolaris Complex
An unusual collection of northern Australian endemics, these plants are characterized by long, hairy petioles, small traps at the tips, a frustrating hot summer dormancy state, and the capacity to freely hybridize amongst each other. The Petiolaris group also boasts the only sundew currently known that does not remain carnivorous throughout its lifetime.
Possessing some of the smallest species in the genus, and unique among sundews in reproducing primarily through unusual modified organs known as gemmae, the Australian pygmy sundews are among the largest subsections of the genus. These species are famed for also having large and variable flowers, with shades of orange, metallic, pink, maroon, and many other colors known.
South African Species
The Cape of South Africa is a unique floral kingdom not just where carnivorous plants are concerned. Separated from the rest of Africa by desert and mountain ranges, a whole host of endemic species has evolved here. Winter-growing sundews abound, including species with the largest flowers in the genus and unique taxa that are more closely related to the genus' relative Dionaea (the Venus Flytrap) than most other sundews.
Australia is the sundew hotspot, and the tuberous plants are another nigh-endemic group to this region. Going dormant in the hot summer season and dying back to small, fleshy corms underground, the tuberous group is divided into three distinct categories: the flat rosetted species, climbers and scramblers, and the fan-leaved tuberous species. All tend to have either thick fleshy leaves and stems or strange peltate leaves, many with bright flowers to rival the pygmies in color and variability, and this group boasts some of the largest sundews on the planet.