The Carnivorous Plant Society - Drosera

Drosera - Sundews

Plant Genus: Drosera

Common Name: Sundew

Number of Species: 160 +

Place(s) found naturally: Present in all continents except Antarctica

Drosera (Droseraceae)

D. hamiltonii

Introduction: The genus Drosera has around 160 species, found, all over the world. In fact, save from the frozen Arctic and Antarctic regions, no continent is without Drosera. In the UK, we have three native species: imagine - CPs on your doorstep! These are not the tropical jungle plants most people associate with carnivorous plants but rather they are small easily missed plants growing on wet heath lands and boggy areas. Elsewhere in the world Sundews inhabit areas that are either wet all year round or just for part of the year. Many Sundews have developed strategies to enable them to survive seasonal droughts.

The common name for the plant is the Sundew, so called because the leaves are covered with a dewy substance that glistens in sunlight. Sundews are rosette-forming plants with glands protruding from the surface of the leaf. At the end of each of these glands is a drop of sticky mucilage, and these double as both lure and snare for insect prey.

Trapping method: Imagine you are a flying insect, happily soaring over picturesque savannah in the warm sunshine. Out of the corner of your compound eye, you spot what appear to be drops of luscious nectar glistening in the light, begging you to take a taste. With a spring in your step (or wings, I suppose!) you descend towards the attractive jewels, and as you get closer you begin to smell that sweet smell while beginning to imagine the gratifying taste. Closer still and you can almost touch the nectar as it seemingly expands in front of your eyes. And then, just as you touch down in an apparent heaven on earth, your leg becomes a little stuck on the nectar. Gleefully, you try to pull it free to begin to gorge on the bounty of nectar before you, but another leg gets stuck; and another; and another.

D. slackii Flower

In panic, you try frantically to escape the clutches of this 'killer nectar' by beating your wings hard, but your legs are stuck firm. Your wings are stuck now, and it seems as if the plant is moving to encase you. Still struggling, you find yourself becoming more and more confined. There is a burning sensation across your wriggling body, as the plant begins to excrete digestive enzymes - the life is literally being sucked out of you. If you are lucky, you'll suffocate quickly. If not, you are subjected to a slow, lingering death. Welcome to the land of the sundews.

Although the above description may sound like a work of insect horror fiction, it is in fact near reality. Although as we will see later there are many types of sundew, the trapping mechanism is common across them all. The 'nectar' on the end of the glands is sticky liquid glue which is capable of ensnaring an insect larger than the leaf itself. Once prey becomes stuck on one of these blobs of glue, any frantic struggling will simply cause it to come into further contact with neighbouring glands, pinning the animal to the leaf. The longer trapping glands fold from the outside of the leaf in towards the centre to ensure the digestive enzymes reach the trapped insect. Some species have even evolved to fold the leaf itself around the victim, thus ensuring maximum contact with the victim. For most insects, death is caused by suffocation since the breathing holes on the side of the insect soon become clogged with mucilage.

Once prey is pinned down, the leaf secretes digestive fluids from sessile glands along the body of the leaf. These work on reducing the fleshy internal part of the insect into a nutrient soup which is subsequently absorbed by the plant. Once digestion and absorption is complete, the leaf returns to its ready state, leaving to dried exoskeleton to be washed away by rainfall, or simply left as a macabre warning to other insects.

D. slackii

Types of Drosera: Sundews can be conveniently divided into groups roughly determined by their growth form and environmental conditions.

Temperate species: These sundews form winter resting buds called hibernacula during the winter months to protect themselves from the effects of these cold temperatures. All three Drosera species native to the UK are in this group: D. rotundifolia, D. anglica and D. intermedia. Also grouped here is the two varieties of D. filiformis, the thread leaf Sundews plus several other North American native species.

South African species: South Africa (SA) is home to so many endemic species of sundew that it may be fair to class them separately although there are many species or similar species found in other southern African countries.

The species can be loosely divided into summer or perennial growers. The plants generally are active from spring through to autumn though if conditions are perfect they can grow at any time of the year. Often these plants survive winters simply by reducing their growth race but in colder areas the plants can survive by their fleshy roots.

Examples from this section are D. capensis from the Cape region of SA, which has strap shaped leaves held semi-erect on long petioles. D. aliciae from the same region has wedge-shaped ground hugging leaves forming a rosette. D. slackii (named after Adrian Slack) was discovered in South Africa in the early 1980s. Other species include D. cuneifolia, D. collinsiae and D. dielsiana amongst others. One exceptional species, which fits in this section better than anywhere else, is D. regia - the King sundew. This species is rare in cultivation and rarer in the wild, but so unique and beautiful with large, stiff sword-shaped leaves stretching for up to 60cm (around 2 feet)

D. adelae

The other section contains the winter growers. These species grow in areas that are dry in the summer but wet in the winter. During the summer the above ground portions of the plants dry off and die but the plant’s survival is ensured by the fleshy roots that allow the plants to grow back once the winter rains return.

Examples include D. cistiflora which forms tall plants with long arm-like leaves growing alternately from the main stem and large flowers in a range of colours.

Other rosette-forming species: These plants are found all over the world, and some species are pan-continental. They form rosettes of ground-hugging leaves and are in active growth all year round. Species in this category include D. spatulata, D. capillaris, D. hamiltonii and D. montana amongst others.

D. mannii

Pygmy species: These species are - guess what - small! On the whole, they have rounded leaves with glands on the end of petioles held in a rosette fashion, and most are less than 2.5cm (1 inch) in diameter. The majority are found in Australia, where they go dormant during the dry summer months and come into active growth during the wetter winter. There are many species which fall into this category - around forty - and these include D. scorpioides, D. pulchella, D. mannii and D. callistos.

Tuber-forming species: This group of plants are also found mostly in Australia, and survive the dry summers by forming tubers under the ground. These species are popular with collectors since they flower at a time of the year when most CPs are dormant. Examples in this large category are D. peltata, D. gigantea, D. macrantha, D. stolonifera, D. ramellosa, D. macrophylla and D. whittakeri amongst others.

D. prolifera

North Queensland species: Grouped together here are three species which share remarkably similar conditions and can be found no where else on Earth! They are: D. adelae, D. prolifera and D. schizandra.

Fork leaved species: These species found in eastern Australia, with one species growing in New Zealand. Debate rages over whether or not all the plants with forked leaves are forms of D. binata, but currently D. dichtoma and D. multifida are considered distinct enough to be separate species. Each species listed here has at least one other form, and a popular hybrid is between D. dichtoma "Giant" and D. multifida "Extrema". A particular form was selected by Adrian Slack, who named it D. ‘Marston Dragon’.

In the Wild: With such a wide geographical spread, it is not surprising to find that some species are thought by some as CP weeds, while others are extremely endangered. Nevertheless, it should be stressed that no matter how common any plant, be it carnivorous or not, are in an area, they should not be removed by any collectors. Exceptions of course occur when those removing plants are botanists or connected scientists doing so for research and/or conservation.

D. capensis Red form

Cultivation: With the growth in tissue culture, even the rarest Drosera in the wild is either available or soon to be available for cultivation. In mainstream garden centres across the UK you are likely to find D. capensis, D. aliciae and possibly D. adelae on sale at some point during the year, but over and above that it is unlikely you will find much. However, many private nurseries and growers in the UK seem to be able to churn out batch after batch of sundews, so the chance to expand your collection is always there!

Since the geographical range of these plants varies hugely, so do their cultivation requirements. As a general rule, a soil mix of two parts sphagnum moss peat to one part sand or perlite will suit most species. It is also possible to grow these plants peat-free. Sunny conditions are essential and watering should be done using the tray method.

Environmental status: Many areas where Sundews grow are already threatened, mainly due to habitat loss. However, most Drosera species do not have endangered status and there are no specific restrictions in international trade except those imposed by host nations. Where the habitat still exists most Drosera species are common though due to the small size of the plants they are often difficult to locate.

For more plant information check out Rick Walker's CP Database