Drosera

The genus *Drosera*, commonly known as sundews, represents one of the largest groups of carnivorous plants.

Scientists have identified at least 194 different species within this genus. These plants are found on every continent except for Antarctica.

Sundews are specialized for nutrient uptake through carnivory. This behavior allows them to supplement their diet when they grow in soil that lacks essential minerals. Most species are perennial herbaceous plants. They often form upright or prostrate rosettes. Some climbing species, such as *Drosera erythrogyne*, can grow much longer stems. Remarkably, some sundews can reach a lifespan of 50 years.

The mechanism for capturing prey is a sophisticated biological process. The leaves are covered in glandular trichomes, which are tiny, hair-like structures. These structures include stalked glands that secrete a sweet, sticky substance called mucilage. This mucilage acts as a lure to attract insects.

When an insect touches the mucilage, it becomes ensnared. The prey may die from exhaustion or asphyxiation as the liquid clogs its spiracles, which are breathing holes.

Once the insect is trapped, the plant secretes various enzymes, including esterase, peroxidase, phosphatase, and protease. These enzymes dissolve the insect into a nutrient-rich mixture. This mixture is then absorbed through the leaf surfaces. Some species also use sessile glands, which are glands without stalks, to absorb this nutrient soup.

Sundews exhibit a remarkable movement known as thigmonasty. This is a rapid response to physical touch.

When a tentacle is stimulated, it fires action potentials that travel to the base of the tentacle. This triggers auxin-mediated acid growth. The plant hormone auxin causes protons to be pumped into the cell wall. This reduces the pH and makes the cell wall more acidic. The acidity relaxes a protein called expansin. This allows the cell to increase in volume through osmosis and turgor. As cells expand at different rates, the tentacles bend toward the center of the leaf. Some species, like *Drosera glanduligera*, can move in tenths of a second. Others, like *Drosera capensis*, can curl their entire leaf around prey within 30 minutes.

There are several distinct growth forms among sundews. Temperate sundews, found in North America, Europe, and Northern Asia, often form a hibernaculum. This is a tight cluster of unfurled leaves used during winter dormancy.

Subtropical sundews maintain growth all year due to stable climates. Pygmy sundews are a group of about 40 Australian species. They are characterized by miniature size and the formation of gemmae for asexual reproduction.

Tuberous sundews, including nearly 50 Australian species, form underground tubers to survive dry summers.

Finally, the *Drosera petiolaris* complex consists of tropical Australian species that live in warm, wet conditions.

The study of these plants has a rich history. Carl Linnaeus first published the genus in his work *Species Plantarum*. The name *Drosera* comes from the Greek word *drosos*, meaning dewdrops. This refers to the glistening mucilage that looks like morning dew.

Charles Darwin performed much of the early research on the genus. He conducted extensive experiments with *Drosera rotundifolia*. His work provided the first confirmation that plants could indeed be carnivorous. In an 1860 letter, Darwin expressed how deeply he cared about studying *Drosera*.

Sundews also produce specialized flowers to ensure successful reproduction. These flowers are typically held on long stems far above the carnivorous leaves.

This separation is an adaptation to prevent the plant from accidentally trapping its pollinators. The flowers are often radially symmetrical and possess five parts. Most flowers are white or pink, though Australian species can be orange, red, yellow, or violet. The flowers are often heliotropic, meaning they move to follow the sun's position in the sky. The ovary of the flower eventually develops into a seed capsule containing many tiny seeds.

While their leaves are highly developed for feeding, the root systems of most sundews are relatively simple. These roots are often weakly developed and serve primarily to anchor the plant and absorb water.

They are generally not used for significant nutrient uptake. However, some species use their roots for other purposes. For example, certain South African species use roots for food storage. Some Australian species use underground corms to survive dry seasons. In some cases, roots even assist in asexual propagation by sprouting new plantlets along their length.