The Drosera genus, commonly known as sundews, is one of the most diverse groups of carnivorous plants, encompassing over 150 species found across nearly every continent except Antarctica. These perennial herbs are famous for their deceptive leaves, which are covered in glistening, stalked hairs that resemble morning dew. This characteristic appearance gives the plant its name, hinting at the sticky trap that lies in wait for insects. Sundews have developed a specialized method for supplementing their diet in harsh environments.
The Anatomy of the Sundew
The sundew’s trapping mechanism is part of its leaf structure, covered in specialized, hair-like appendages called glandular trichomes. These tentacles vary in length and are tipped with a gland that secretes a droplet of clear, viscous fluid. The leaves themselves can display a variety of growth forms, ranging from flat, ground-hugging rosettes to upright, stem-forming types.
The tentacles are highly sensitive and designed to move, a capacity most pronounced in the longer tentacles near the leaf margins. These outer tentacles can be ten times longer than the inner ones, creating a three-dimensional trap surface. The mucilage droplet is a sticky, polysaccharide solution that serves as both a lure and an adhesive. The plant’s ruby-red color and glistening droplets effectively attract small flying insects like gnats and fruit flies.
The Mechanics of Trapping and Digestion
When an insect lands on the leaf, it instantly becomes mired in the sticky mucilage. The insect’s struggle stimulates sensory cells within the trichomes, triggering a rapid response. This stimulation causes the tentacles closest to the prey to slowly bend inward, securing the insect and pushing it toward the leaf center. In some species, marginal tentacles coil around the prey within minutes to maximize contact with the digestive surface.
Once the prey is secured, the plant initiates digestion by releasing specialized enzymes, primarily proteases, from the glandular heads. These enzymes break down the insect’s soft tissues, dissolving proteins and nutrients. The mucilage is slightly acidic (pH around 5), which aids the breakdown process. The plant then reabsorbs the nutrient-rich fluid, which contains nitrogen and phosphorus, leaving only the insect’s hard exoskeleton behind.
Why Sundews Are Carnivorous
The carnivorous habit of the sundew is not a means of obtaining energy, which the plant still derives through photosynthesis. Instead, it is a survival strategy to acquire essential mineral nutrients that are scarce in their native habitats. Sundews thrive in highly specific environments such as bogs, fens, and acidic wetlands, where the soil is waterlogged and poor in nutrients.
The acidic, peaty substrate in these areas hinders the absorption of minerals by the plant’s roots. Specifically, the soil in these wetland habitats is deficient in nitrogen and phosphorus, two macronutrients necessary for plant growth. By capturing and digesting insects, the sundew bypasses this nutrient poverty and obtains these compounds directly from its prey. This adaptation allows sundews to flourish in ecological niches where other plants cannot compete.
Growing Sundews at Home
Successfully cultivating sundews requires replicating the harsh, nutrient-poor conditions of their natural environment with high precision.
Soil Requirements
The correct soil composition must be a nutrient-free and highly acidic mix, typically a blend of sphagnum peat moss and horticultural-grade sand or perlite. Standard potting soil or garden soil is completely unsuitable, as the mineral salts and fertilizers quickly poison the plant’s sensitive root system.
Watering and Light
Watering must be done exclusively with distilled water, rainwater, or water purified through reverse osmosis. Tap water contains dissolved minerals and salts that accumulate in the soil over time and burn the roots, inhibiting mucilage production. The best method is the tray method, where the pot is placed in a saucer of water, allowing the plant to wick up moisture and keeping the soil consistently damp. Sundews require intense light, needing at least six hours of bright, direct sunlight daily to produce the characteristic red coloration and glistening dew drops.
Temperature and Dormancy
While many tropical species grow year-round in warm temperatures (up to 85°F), temperate sundews require a cool winter dormancy period. They often need temperatures to drop below 50°F for a few months to survive long-term.