Carnivorous Plant - Sundew

In short: Sundews (Drosera) are carnivorous plants that trap insects with sticky mucilage on leaf tentacles, digest them with enzymes and absorb the released nutrients through the leaf. The genus had 188 counted species in 2008, and over 50% of known species grow wild in Australia.

Sundews - Drosera are one of the largest genera of carnivorous plants. In 2008, 188 species of these carnivorous plants were counted. They are members of the Droseraceae family which captures and digests insects using mucilage glands on the leaf surface. Insects or small vertebrates serve as a supplement in poor soils with low nutrient content. All species of sundews can be naturally found on every continent except Antarctica.

The botanical name comes from the Greek δρόσος "drosos" = which literally means dew or dew drops. The name is derived from the glistening transparent drops of mucilage that are at the tip of each tentacle.

Sundews are mostly perennial plants and grow very quickly. Sundews measure from a few cm to tens of cm in height. Climbing species can reach up to 3m. Some plants can live up to 50 years!

What are sundews?

Sundews are characterized by tentacles with glands secreting a sticky secretion that covers tiny projections on the plant's leaves. For catching and digesting prey, stalked glands secreting a sweet sticky substance are usually used. This attracts and glues insects. The prey either succumbs to death by exhaustion or suffocation caused by the sticky substances that surround it. Death usually occurs within an hour and fifteen minutes. Meanwhile, the plant secretes esterase, peroxidase, phosphatase and protease enzymes. These enzymes break down the insect and release nutrients from it. The resulting substance is then absorbed through the leaf surface and the nutrients are used as supplementary nutrition. In this way, carnivorous plants essentially 'fertilize themselves'.

All sundews can adapt their shape to current needs, for example to better wrap around prey. However, the movement is relatively slow, in the order of hours. But some species can react even in the order of seconds (for example Drosera burmannii). The tentacles are extremely sensitive to any touch and when irritated, they bend towards the center of the leaf. According to Charles Darwin, contact of a small mosquito's leg with one tentacle is enough to cause irritation. This reaction to touch is called thigmonastic. In addition to the tentacles, some species can bend the leaf blade to varying degrees to maximize contact with prey. However, this movement is much slower and takes about 30 minutes.

What sundews look like

The flowers of sundews, as with almost all carnivorous plants, are held high above the leaves on a long stem. The flowers are isolated from the traps so that pollinators can fly to them as safely as possible. Most inflorescences are buds whose flowers open only for a short period. The flowers open in response to light intensity (often opening only in direct sunlight). The flowers are usually white or pink and adjust their direction to the movement of the sun across the sky. This probably testifies to the poor conditions in which sundews naturally live. Nevertheless, sundews are declining worldwide, especially due to the destruction of their natural habitats. These are mainly swamps, marshes or peatlands.

The root system of most sundews is very poorly developed. It serves primarily for water absorption and anchoring the plant in the soil; when it comes to nutrient uptake, the roots are almost useless. Several South African species use their roots for food storage. Some species have a fibrous root system that remains alive during frosts even if the upper part of the plant dies. Species such as Drosera adelae and Drosera hamiltonii use their roots for asexual reproduction.

Many sundew species are monoecious. Sundews produce large quantities of very small seeds. Seeds of more exotic species germinate in response to moisture and light, while seeds of temperate species require moisture and cold. Vegetative reproduction occurs naturally in some species whose roots are very close to the soil surface (e.g., Drosera adelae and Drosera hamiltonii). A new plant can also sprout from older leaves that touch the ground.

Where to Find Sundews

The range of these carnivorous plants extends from Alaska south to New Zealand. Over 50% of all known species live in the wild in Australia, at least 20 in South America, and over 20 species in South Africa. A small proportion of carnivorous plant species occur naturally in North America and Europe.

Many medicines also contain active ingredients found in sundews, such as certain flavonoids (kaempferol, myricetin, quercetin, hyperin), quinones, carotenoids, resins, tannins, and several acids (butyric, citric, malic, ascorbic). Australian Aborigines have found another use, considering sundews a delicacy. The tubers of some species were used as a textile dye. In the Scottish Highlands, a liqueur is made from Drosera rotundifolia according to an ancient recipe. In countries such as Germany, Austria, Switzerland, the Czech Republic, Finland, Hungary, France, and Bulgaria, sundews are protected. The situation is currently critical, especially in North America, where the draining of swamps is destroying their natural habitat.