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DROSERACEAE is a family of flowering plants . The family is also known as the sundew family. It is a small family of carnivorous plants , which consist of approximately 180 species in three extant genera:
* 1 Description
* 2 Phylogeny * 3 References * 4 External links
Most of the members of
Drosera is one of the largest genera of carnivorous plants, and individual species vary extensively in their specific morphology. Common to all members of Drosera are highly modified leaves lined with tentacle-like glandular trichomes . At the end of each trichome, a bead of highly viscous mucilage is secreted, which resembles a drop of dew. The mucilage is a fairly pure aqueous solution of acidic polysaccharides with high molecular weights, which makes the mucilage not only highly viscous, but also very sticky, so much so, a single drop of mucilage may be stretched to lengths of up to a meter and cover one million times its original surface area. Insects and other prey animals are attracted by the smell of this mucilage and become stuck in it. Such snares are termed “flypaper traps”, but the trapping mechanism of sundews is often erroneously described as “passive”. In fact, sundew traps are quite active and sensitive, and the disturbance of one or a few trichomes quickly triggers an action potential that stimulates the rapid movement of other trichomes toward the prey. The leaf then curls in on itself, enveloping the prey for digestion.
Dionaea muscipula , better known as the
Venus flytrap , is a globally
famous carnivorous plant and according to
Aldrovanda vesiculosa , also called the waterwheel plant, is less well-known than its relative Dionaea muscipula, but the two have similar trap structures. 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.
Despite some debate, taxonomists have tended to include at least two of the three genera, and, in general, all three, in this family since at least 1906. Separate families for Dionaea and Aldrovanda have been proposed in the past. These were Dionaecae, proposed in 1933, and Aldrovandaceae, proposed in 1949. Ultimately, molecular and morphological evidence support the inclusion of all three, and also shows the two genera with traps that snap shut (Dionaea and Aldrovanda) are more closely related to each other than to Drosera, suggesting snap traps evolved only once.
In the past, Drosophyllum lusitanicum has been included in this family. Drosophyllum, another monotypic genus, exhibits a flypaper-type trap similar to those of Drosera, but Drosophyllum does not actively curl its leaves to envelop captured prey animals. This important morphological distinction led researchers to question the validity of this taxon’s placement in Droseraceae. Other significant trait differences in Drosophyllum include pollen structure, trichome anatomy, and a woody stem with a deep taproot. Ultimately, Drosophyllum was shown to be more closely related to the carnivorous liana Triphyophyllum and the noncarnivorous liana Ancistrocladus , and is, thus, classified elsewhere (to be specific, its own monotypic family Drosophyllaceae ). Recent molecular and biochemical evidence (see the AP-Website) suggests the carnivorous taxa in the order Caryophyllales (the families Droseraceae, Drosophyllaceae , Nepenthaceae , and the species Triphyophyllum peltatum ) all belong to the same clade , which does not consist only of carnivorous plants, but also of some noncarnivorous plants such as those in the family Ancistrocladaceae .
The fossil record of Droseraceae