Droseraceae

Lore & Background

Droseraceae are carnivorous herbaceous plants that may be annuals or perennials. Their leaves are alternate and adaxially circinate, with at least one leaf surface containing hairs with mucilage-producing glands at the tip. Their flowers are bisexual, usually with three carpels and five sepals, petals and stamens. Despite being carnivorous, their flowers are insect-pollinated, typically with white to purple flowers that close at night. They produce small seeds that are dispersed by wind and water. Most members are in the genus Drosera, the sundews, which trap prey by secreting a sticky substance from hairs on their leaves. Dionaea and Aldrovanda both use snap-traps that close rapidly when the leaves are disturbed. Dionaea is terrestrial, while Aldrovanda is strictly aquatic. The family can supplement nutrient intake, especially nitrogen, by capturing and digesting small animals such as insects, allowing them to thrive in nutrient-deficient areas like sphagnum bogs. The family has a rich fossil record, the richest of any carnivorous plant family. Molecular evidence shows that the two genera with snap traps (Dionaea and Aldrovanda) are more closely related to each other than to Drosera, suggesting snap traps evolved only once.

Reader's Guide

Droseraceae holds a significant place in botanical history as one of the most diverse and well-studied families of carnivorous plants. The family includes approximately 180 species across three extant genera: Drosera (sundews), Dionaea (Venus flytrap), and Aldrovanda (waterwheel plant). These plants are found on all continents except Antarctica, thriving in nutrient-poor environments by supplementing their diet with captured insects and other small animals. The family's trapping mechanisms are particularly noteworthy. Drosera species use flypaper traps with sticky mucilage that can be stretched to lengths of up to a meter, while Dionaea and Aldrovanda employ rapid snap-traps. The Venus flytrap's trap can begin closing as fast as 0.4 seconds after stimulation. Aldrovanda, an aquatic plant, closes its trap about ten times faster than Dionaea and requires only one stimulus to trigger closure, compared to two for Dionaea. Taxonomically, the family has undergone revision. Historically, genera such as Drosophyllum, Byblis, and Roridula were included, but molecular and morphological evidence led to their reclassification. Today, only the three extant genera remain, forming a monophyletic group within the order Caryophyllales. The origin of carnivory in the family's ancestors has been dated to 85.6 million years ago, with snap-traps evolving 48 million years ago. Darwin correctly concluded that carnivory in plants was convergent, a view now supported by molecular studies showing carnivory evolved at least six times in angiosperms.

Did You Know?

• The Venus flytrap (Dionaea muscipula) can close its trap as fast as 0.4 seconds after stimulation.
• Aldrovanda vesiculosa, the waterwheel plant, is a free-floating, rootless aquatic plant whose trap closes about ten times faster than that of Dionaea.
• The mucilage of Drosera can be stretched to lengths of up to a meter and cover one million times its original surface area.
• Fossil pollen of Droseraceae is the richest of any carnivorous plant family.