Droseraceae

The Droseraceae are a specialized family of carnivorous flowering plants. They are commonly known as the sundew family. This group includes approximately 180 different species. These plants are unique because they supplement their nutrients by capturing small animals. They often live in nutrient-deficient environments, such as sphagnum bogs. In these areas, the soil lacks enough nitrogen for normal plant growth. By digesting insects, Droseraceae plants can obtain the nitrogen they need to thrive. They are found on every continent except Antarctica.

Most species in this family belong to the genus Drosera, or sundews. Sundews use a mechanism called a flypaper trap. Their leaves are lined with many tiny, tentacle-like hairs called glandular trichomes. Each trichome secretes a highly viscous mucilage at its tip. This substance is an aqueous solution of acidic polysaccharides with high molecular weights. To an insect, these droplets look like morning dew. The mucilage is incredibly sticky. A single drop can be stretched to a length of one meter. This stretch covers one million times the original surface area of the drop.

While the flypaper trap may seem passive, it is actually quite active. When an insect touches the trichomes, it triggers an action potential. This is an electrical signal that moves through the plant. This signal stimulates other trichomes to move rapidly toward the prey. The leaf then curls inward to envelop the insect for digestion. This active movement helps ensure the prey cannot escape. This process allows the plant to turn a simple sticky surface into a sophisticated hunting tool.

Other members of the family use a different method called a snap-trap. The most famous is the Venus flytrap, or Dionaea muscipula. This is a terrestrial plant with highly modified leaves. Inside the trap, there are three large trichomes. For the trap to shut, two of these hairs must be stimulated within a specific timeframe. Once triggered, the trap lobes flip from a concave to a convex position. This movement can begin just 0.4 seconds after stimulation. The entire closing process is usually completed within one second.

A second snap-trap user is the waterwheel plant, known as Aldrovanda vesiculosa. This plant is strictly aquatic and floats freely without roots. Charles Darwin once described it as a miniature aquatic version of the Venus flytrap. While the structures are similar, the waterwheel plant is much faster. Its trap closes about ten times faster than the Venus flytrap. Unlike the Venus flytrap, the waterwheel plant only requires a single stimulus to trigger the snap.

The history of studying these plants involves many famous scientists. Carl Linnaeus named the genus Drosera in 1753. The name comes from the Greek word "droseros," which means dewy. In 1875, Charles Darwin called the Venus flytrap one of the most wonderful things in the world. For a long time, scientists debated how these traps evolved. Darwin believed that carnivory in plants was a result of convergent evolution. This means different plants evolved similar traits independently.

Modern molecular studies have provided much clearer answers. We now know that carnivory in the ancestors of Droseraceae began about 85.6 million years ago. The evolution of the snap-trap occurred much later, about 48 million years ago. Evidence suggests that the snap-traps in Dionaea and Aldrovanda evolved only once. This is because they are closely related through molecular links. Scientists believe the family may have started with simple flypaper traps. Over millions of years, these evolved into moving tentacles and eventually into the rapid snap-traps we see today.