toward the prey. The leaf then curls in on itself, enveloping the prey for digestion. Four Drosera subgenera are recognized today: subgenus Regiae and subgenus Arcturia are each monotypic (D. regia and D. arcturi, respectively), and the remaining Drosera are divided into two clades, subgenus Ergaleium and subgenus Drosera. Dionaea Dionaea muscipula, better known as the Venus flytrap, is a globally famous carnivorous plant and according to Charles Darwin, "one of the most wonderful in the world." The leaves of Dionaea are also highly modified and form a "snap-trap" that quickly shuts when a stimulus is detected. Three large trichomes extend outward on the inner surface of the trap. Two of these three hairs must be stimulated within a certain amount of time to trigger the trap. The trap closes as the result of a flipping of the trap lobes from a position where the exterior of the trap is concave to one where the exterior is convex. This movement can begin as soon as 0.4 seconds after stimulation and can be completed after one second. Aldrovanda Aldrovanda vesiculosa, also called the waterwheel plant, is a free-floating, rootless, aquatic plant. It is less well-known than its relative Dionaea muscipula, but the two have similar trap structures. In 1875, Darwin described Aldrovanda as "a miniature aquatic Dionaea". The trap of Aldrovanda is aquatic and is smaller and faster than that of Dionaea. In addition, while two stimuli are required to close a trap in Dionaea, only one is required in Aldrovanda. The trap of Aldrovanda closes about ten times faster than that of Dionaea. Etymology The type genus for the Droseraceae is Drosera, which was described and named by Linnaeus in 1753. The name was derived from the Greek word "droseros", meaning "dewy" or "drops of water". The Principia Botanica, published in 1787, states "Sun-dew (Drosera) derives its name from small drops of a liquor-like dew, hanging on its fringed leaves, and continuing in the hottest part of the day, exposed to the sun." Phylogeny In 1867, Bentham and Hooker placed six genera in the Droseraceae: Dionaea, Aldrovanda, Drosera, Drosophyllum, Byblis, and Roridula. Although these genera had significant differences in leaf and flower morphologies, they were grouped together on the basis of insect traps that appeared to be homologous. In 1922, Byblis and Roridula were moved into a new family, the Byblidaceae (and later further split out, forming the Roridulaceae). In