Sundews

Often called flypaper plants, sundews trap prey using sticky hair-like tentacles on their leaves. Of the genus Drosera, sundews comprise one of the largest groups of carnivorous plants and typically grow in bog habitats, where the soil is low in nitrogen. Loss of habitat due to human development has led to decreasing numbers of sundews in the wild.

Sundews get their nickname from the sticky droplets on the tentacles on their leaves. These droplets, which are produced by glands on the tip of the tentacles, glisten in the sun like dew. The glands also produce nectar, which attracts prey; a strong adhesive to capture insects; and enzymes to digest prey. Insects that are snared by the sticky adhesive are gripped by tentacles and smothered. Prey usually die within fifteen minutes, while digestion may take weeks.

Background

Carnivorous or insectivorous plants are adapted to catch and digest insects and, in some cases, animals. They feature a wide variety of traps, such as sticky surfaces and pitchers, which are compartments that insects enter but cannot leave. More than six hundred species of carnivorous plants have been discovered, with the most well-known being the Venus flytrap (Dionaea muscipula). These plants have saucer-like traps that snap shut and tentacles that prevent prey from escaping. Other varieties are pitcher plants, which have deep wells containing digestive fluid. Large tropical pitcher plants will even digest mice and other small animals. After a carnivorous plant catches prey, it is broken down by enzymes or bacteria, and the plant absorbs the nutrients and salts. Most carnivorous plants grow in poor soil, so although they make food using light and water by photosynthesis, they cannot survive without the nutrients they acquire through carnivory, or eating meat.

The origin of sundews is unclear, but the majority of Drosera species appear to have descended from a plant that grew in Australia tens of millions of years ago. This plant was very similar to Drosera spatulata, the modern spoon-leaved sundew. Like all sundews, its leaves are arranged in a rosette pattern. Drosera probably reached North America from Australia by way of Asia and from there spread to South America. Birds were likely responsible for the plant’s additional migration.

Researchers have studied the genomes of carnivorous plants in Australia and compared them to insect-eating plants around the world. They have concluded that carnivory developed multiple times across millions of years. This is known as convergent evolution, when organisms not closely related but living in similar habitats evolve similar traits. What these varied plant species had in common was an environment with low-nutrient soils. Carnivory became possible when an ancestor plant created a second copy of its entire DNA, or genome. The bonus set of leaf and root genes was free to adapt to other uses, while the original set grew leaves and roots. Once plants were receiving nutrition from prey, they no longer needed to develop extensive roots and leaves, so some of those genes disappeared. Most modern carnivorous plants have fewer genes than other types of plants.

Researchers have analyzed the digestive enzymes used by pitcher plants and other carnivorous plants. They discovered several dozen proteins, many of which are similar to those in other flowering plants. In non-carnivorous plants, the proteins are defensive. For example, some enzymes protect against fungi by breaking down a polymer found in the cell walls of fungi. Insect exoskeletons are made of this same chemical, chitin. Carnivorous plants seem to have repurposed chitin to digest prey.

Overview

The approximately 150 species of sundews are variable in size and shape. Some are low to the ground, while many varieties reach heights up to 10 inches (25 centimeters). Still others are much taller and resemble vines. Some species are threatened or endangered in some states; the greatest threat to these plants is loss of boggy habitat.

Sundews are found throughout the United States, although they do not grow in some parts of the Southwest. Their preference for bog habitats keeps them in close proximity to mosquitoes, which make up a large part of their diet. Species grow in South America, Australia, New Zealand, and other tropical and temperate areas.

Most sundews are perennials. They usually have leaves smaller than 1 inch (2.5 centimeters) in diameter that are in a rosette arrangement, although some species have long, thin, whip-like leaves. One of this variety is the King Sundew, Drosera Regia. This very rare plant grows only in a few colonies in South Africa. Its sword-shaped leaves can grow to nearly 2 feet (30 centimeters) in length. The leaves on young King Sundew plants can twist around prey in knots. The upper surfaces of the leaves on most sundews are covered with tentacles called trichomes, which produce a sticky glue. The leaves roll up to entrap and digest insects that become stuck to the glue. Many have small white or pink flowers with five petals that bloom atop a curving stem.

Reproduction varies; some species can self-pollinate, producing high volumes of seeds after the flowers close. Others reproduce by producing seeds through pollination, which requires the presence of both male and female plants of the same species within an area. Some plants will sprout plantlets on leaves that touch the ground. Tuberous sundews can produce new plants from corms, which are underground stems. Sundews can also be propagated by taking cuttings of leaves, roots, or crowns, or by growing them from seeds.

Potted sundews require high humidity and a growing medium that is very moist but not wet. A combination of sphagnum peat moss with perlite or lime-free coarse sand may be blended, or special mixes can be purchased from some nurseries. Plants should never be fertilized, and water should be distilled or rainwater to prevent mineral buildup in the pot. Sundews also require a great deal of light, and some may need a dormant season in winter, when they should be moved to a sunny window in an unheated garage or similar protected location.

Bibliography

Brittnacher, John. “Carnivorous Plant Digestion and Nutrient Assimilation.” International Carnivorous Plant Society, www.carnivorousplants.org/cp/carnivory/digestion. Accessed 25 Nov. 2024.

Brittnacher, John. “Drosera Phylogeny.” International Carnivorous Plant Society, Jan. 2011, www.carnivorousplants.org/cp/evolution/DroseraPhylogeny. Accessed 25 Nov. 2024.

Brittnacher, John. “Drosera Spatulata Species Complex.” International Carnivorous Plant Society, Jan. 2019, www.carnivorousplants.org/cp/taxonomy/Droseraspatulata. Accessed 25 Nov. 2024.

Callaway, Ewen. “How Plants Evolved into Carnivores.” Scientific American, 6 Feb. 2017, www.scientificamerican.com/article/how-plants-evolved-into-carnivores/#. Accessed 25 Nov. 2024.

"Carnivorous Plant Care: Sundews." New York Botanical Gardens, 22 Nov. 2024, libguides.nybg.org/c.php?g=654975&p=4597461/. Accessed 25 Nov. 2024.

“The Carnivorous Plant That Feasts on Mice.” Smithsonian Magazine, www.smithsonianmag.com/videos/category/science/the-carnivorous-plant-that-feasts-on-mice/#. Accessed 25 Nov. 2024.

Lincoln, Diane. “Here’s How Plants Became Meat Eaters.” Live Science, 1 June 2020, www.livescience.com/how-carnivorous-plants-evolved.html. Accessed 25 Nov. 2024.

“Sundews.” National Wildlife Federation, www.nwf.org/Educational-Resources/Wildlife-Guide/Plants-and-Fungi/Sundews#. Accessed 25 Nov. 2024.

“Sundews (Drosera).” California Carnivores, www.californiacarnivores.com/pages/sundews-drosera. Accessed 25 Nov. 2024.