Eurasian & North American Sundew

The Genus Drosera

The genus Drosera contains approximately 250+ species and is distributed on all continents except Antarctica. The little “+” accounts for the fact that new species are still being described, particularly from regions where many species are already known.

The major hotspots are Australia with 165+ species, sub-Saharan Africa with 36+ species, and South America with 43+ species. North America and Eurasia together hold 12 species. Thus, this is a genus primarily distributed in the tropics and subtropics of the Southern Hemisphere.

Most sundew species are restricted to very small areas, while the sundews we know from our own nature are exceptions within the genus, as they have enormous natural ranges. More about this under the species descriptions.

Europe, with three species and two natural hybrids, is rather poor in species. North America fares a little better with eight species and a number of hybrids – including the same species found in Europe.

The genus Drosera is divided into seven groups, based on growth forms:

• The temperate species that form a winter bud.

• South African species that go into summer dormancy. These come from the winter rainfall areas of South Africa. They are adapted to the dry summer period and survive by means of strong root systems.

• Tuberous sundews. Species primarily from Australia, but also a few from New Zealand northwards to Japan. These form tubers with which they endure the dry period. In this group we find species the size and shape of asparagus plants, species that climb several meters up into shrubs, and small rosette-forming species. Many of the most spectacular sundews belong here. They are mainly winter-growing.

• Pygmy sundews. These have their primary distribution in southwestern Australia. Very small species with 0.5–3 cm rosettes, often bearing large, brightly colored flowers. Easy to grow and worth collecting.

• Tropical and subtropical perennial species. A large number of species from across the genus’ Southern Hemisphere range. A well-known example is Drosera capensis, widely grown in cultivation.

• Tropical species that go into summer dormancy. This group is found in tropical northern Australia. Most of them go dormant during the scorching summer and grow in winter.

• Annual species. These occur across most of the genus’ range, except in Europe. Their strategy is a short growth season followed by heavy seed production to survive unfavorable periods. Some may live for several years if conditions are suitable.

The closest relatives of sundews are the Venus flytrap (Dionaea muscipula) and the equally spectacular aquatic plant Aldrovanda vesiculosa.

As one might sense, diversity within the sundew genus is immense. In the following, we will focus on the more or less frost-tolerant species from North America and Eurasia. Thus, all the information to follow applies to this group alone, although, with a solid understanding of the climates in their native regions, many of the principles can be applied to the cultivation of about 80% of all sundew species.

Anatomy of Sundews

Leaves and adaptations for capture and digestion
The plants form rosettes. The leaves consist of a petiole with a leaf blade. On the blade itself, there are numerous more or less stalked glandular hairs that form the basis for capturing small animals. These are called tentacles. The tentacles produce a mucilage droplet that sits at their tips.

When an insect lands on the leaf blade, it comes into contact with many sticky droplets, and as it struggles, it becomes increasingly entangled in the slime. This triggers, in many sundew species, a capture movement. The leaf itself begins to slowly fold around the prey, while tentacles that have not yet touched it are activated on the sides or above the prey, depending on its size.

Flowers

The flowers can be white, pink, or shades in between. In many species, the flowers are small and inconspicuous – this is the case, for example, with our native species. In these, a high degree of self- and wind-pollination occurs, though small beetles are also believed to contribute to pollination.

Others, such as those in the Drosera filiformis group, have large, brightly colored flowers that are frequently visited by insects, especially bees. Drosera tracyi appears to be the only species in our group that relies exclusively on cross-pollination; all others are capable of self-pollination.

The flowers are usually held well above the traps so that the plant does not consume the very insects it relies on for pollination.

The seeds mature in a capsule. The long flower stalks can act like a catapult, hurling the mature, dry seeds into the air. It is assumed that, for several species, the seeds can travel kilometers on the wind. On a smaller scale, one can observe this in a large plant collection, where tiny sundews suddenly appear in unexpected places.

The seeds may also disperse across the surface of floodwaters, establishing new colonies once they settle. For most species, it is sufficient that just one seed germinates – self-pollination ensures the colony’s continuation.

Cultivation Techniques

Sundews have specific needs that must be met, especially regarding light and water. If these are provided, they are easy plants to grow.

Light
Sundews from Europe and North America require a lot of light. Full sun all day is best. They can tolerate less, but in partial shade the plants quickly become pale and lose their attractive red coloration. In deeper shade, they prioritize photosynthesis over insect capture, resulting in pale leaves without mucilage production. If they receive too little light, they weaken and fail to sprout the following spring.

Water
Sundews from the northern group are bog plants. Some grow in slightly drier habitats, others directly in water – and sometimes under water – but they must never dry out.

Rainwater or water from a reverse osmosis system is recommended. One should aim for 0–50 ppm. They can easily survive a few waterings with tap water, but on the list of things that kill sundews, total drying out ranks just above hard, mineral-rich water. The latter eventually raises the acidity of peat, enabling bacteria to break it down and release nutrients – poison for carnivorous plants.

If you do not use the right water, you can forget about cultivating carnivorous plants.

Growing Medium

I primarily grow the plants in unfertilized, unprocessed peat – the same type used for rhododendrons. It can be mixed with perlite or lime-free sand to improve aeration.

Species such as the round-leaved sundew (Drosera rotundifolia) grow well in living sphagnum moss (Sphagnum spp.), which requires similar cultivation conditions. Note that some sphagnum species are rare, while others grow too vigorously and can overgrow your sundews.

Good, compact, common species include Sphagnum papillosum. Much like bonsai, which gains character with age, certain sphagnum species can, over time, form beautiful dense cushions. These, adorned with bright red sundews, are very decorative. I predict that sphagnum cultivation has a great future.

Pots and Bog Beds

The plants can be grown in plastic pots or in specially constructed bog beds in the garden.

Clay pots are not recommended. They rarely tolerate frost if wet – and when growing sundews, they are always wet. They also dry out far too quickly on a hot summer day. Plastic pots are much better, and if bought in good quality, they can last for years. I often use Christmas tree pots when I need containers of a few liters or more; some of these have now been standing outdoors in water for sixteen years.

Many sundews are very small, and the northern species generally have modest root systems. Nevertheless, I often use large pots (2–10 liters), as I like to keep the small species in groups or allow the large species to actually become large. Plants look striking when many are gathered, and the large pots, with their greater soil volume, are better protected against drying out on a hot summer day.

Many sundew species are very hardy and are kept outdoors in pots, fully exposed. The pots are placed in wooden frames lined with pond liner, ensuring a constant water level at the bottom.

Closed pots without drainage holes are less suitable. It is harder to control the water level when you cannot see it, and you cannot flush through the pots as you can with holes. If, in emergencies, the plants have been watered with tap water, it is beneficial to let them be flushed by rain all winter outdoors to restore the natural acidity of the peat.

In greenhouses, the same principles apply, except that I do not place the pots on the ground but on tables holding water. I construct my tables from pallets resting on lightweight concrete blocks. A frame is built on the pallet and lined with pond liner. It can of course be made much prettier if one has the need.

Bog beds are, simply put, larger or smaller artificial bogs established outdoors or in the greenhouse if space – or enthusiasm – allows. They are similar to garden ponds, except that they are filled with peat instead of water. They can be made in any size.

My smallest bog beds are pallet frames lined with pond liner, filled with peat, and placed directly on the ground.
The largest are several meters long and wide, built with heavy decking boards so that the exciting plant communities are raised for closer study. They can also be made sunken, like a typical garden pond.

One can create truly fascinating small ecosystems in bog beds, and sundews are obvious candidates for inclusion.

If one cultivates a living moss surface in bog beds, the moss may over time grow upward, in complete contrast to a rhododendron bed. Thus, one gets more bed volume as time passes, and in principle, they can last forever – interrupted only by the decay of the wood and pond liner, or by one’s own changing interests and circumstances.

Changing Seasons

Most species from this group I grow entirely outdoors, or, for those from the southern United States, in an unheated greenhouse. The greenhouse gives them a longer and warmer growing season than our still rather cool climate can provide, and it also protects against the harshest frosts. –18 °C outside the greenhouse means –8 °C inside my polytunnels, as long as it is only a single cold night.

Extended periods of day- and night frost naturally eat more into the stored heat that a glass or plastic house can retain. However, we rarely experience long frost periods anymore, and often they are quite sunny, which again helps the overall temperature balance.

Many of the southern species fortunately tolerate some frost. Remember, it even snows in Florida from time to time.

Most species form a small winter bud. This can withstand most of the winter’s hardships, but it always does best if protected against the most desiccating winter winds. Outdoors, it is best to leave withered leaves in place, as they protect the plant. One may also cover the winter bud with a little peat or birch leaves. Life outdoors is characterized by good air circulation and frequent, healthy baths in ice-cold rainwater.

In the greenhouse, a different approach to withered leaves is required, as they can become a breeding ground for destructive fungal diseases. Leaves must be removed as early as October, as soon as they have withered. The combination of dead foliage, cold, moisture, and stagnant air is a recipe for disaster for a carnivorous plant grower. Thus, besides keeping the greenhouse meticulously free of dead leaves in winter, watering must be reduced to slightly moist, not wet, pots, and good air circulation is fundamental for successful overwintering.

I keep windows and doors open year-round, except during hard frosts at night or in storms and snowstorms. As soon as these conditions pass, I open again.

Diseases

The fungal diseases mentioned during winter are the biggest problem, and here prevention is better than cure. Should misfortune strike, it is important to remove all infected tissue immediately. Fungal outbreaks progress very quickly and can cost entire plants their lives. The removed material must be taken out of the greenhouse so it does not spread spores further through the system. The affected plant can be topped with a layer of fine, dry, lime-free sand, which helps prevent the disease from spreading further.

Plants kept outdoors are rarely attacked by fungal diseases.

In summer, aphids can be a problem, again primarily in greenhouse-grown plants. The aphids must be removed manually, as sundews cannot tolerate most pesticides. An easy cure is to place the plants outside for a while until the aphids are gone. In summer, all the sundew species described here can be grown outdoors.

One final pest worth mentioning is blackbirds. Both sundews and living sphagnum moss are ideal nest material, and if one has many of these birds around, the plants must be protected from their ravages.

Propagation

Sundews can be propagated in two ways:

1. Sexual reproduction using seeds.

2. Asexual reproduction by dividing a plant, resulting in two or more genetically identical clones of the same plant.

All species produce seeds. Most are self-pollinating, and only Drosera tracyi requires cross-pollination, although it can, in certain cases, be persuaded into self-pollination by transferring pollen from other sundew species. Some of the offspring, however, will then be hybrids.

Seeds can be sown fresh from the capsule, and some species will often germinate immediately.

If seeds are stored dry for a period, species from regions with pronounced frost require stratification to germinate again. The easiest way to achieve this is in an unheated greenhouse, sowing the seeds in March (or earlier) while nights are still frosty.

The reason I sow in the greenhouse rather than outdoors is that the tiny seeds can easily be displaced by raindrops. Seed propagation is easiest to manage in the greenhouse.

If stratified seeds have not germinated by midsummer, there is no point in keeping the pots any longer – the seeds are no longer viable. If one does not wish to accept that they will not sprout, it is advisable to sow something else in the pot, something entirely unlike the first sowing but with the same soil requirements. This way, the contents can be given extra time without wasting space.

I always sow on pure peat in small pots standing in 1–2 cm of water. The seeds must not be covered, as they require light to germinate. The pots are not covered with plastic, as this encourages mold and is otherwise unnecessary for germination. The substrate contains sufficient moisture by itself.

Well-developed plants of most species can be divided. One looks for multiple shoots emerging from the base; each of these can readily be turned into a new plant. This can be done in winter, when the plants have formed winter buds, but also in summer during active growth. Even flowering plants can be divided and will continue growing after a short pause.

The many sundew hybrids are generally sterile. For them, division is the only method of propagation, not seed sowing – with a few interesting exceptions, which will be addressed later in the section on hybrids.

Drosera anglica – Long-leaved Sundew

The long-leaved sundew is the rarest Danish sundew. I know of three populations, but there are more. In nature, it is often confused with the oblong-leaved sundew (Drosera intermedia), which is more widespread, and many reports of the species actually cover a finding of D. intermedia.

The long-leaved sundew can be recognized by its long leaf blades, which are three to four times longer than those of D. intermedia, and more upright.

One should not take the state of the Danish populations as an expression of how rare the species is in general, since it has a distribution stretching from Japan across China, eastern and central Russia, Europe from Scandinavia south to Spain, Italy, and Georgia. In addition, it has a wide distribution in Canada and the United States as far south as California and Colorado, as well as a tropical population in Hawaii.

The species is believed to be an ancient hybrid between Drosera linearis and Drosera rotundifolia. The hybrid between these two is sterile and can be found wherever the two species meet. At some point, a chromosome doubling occurred, and a new fertile species came into existence. Such events also occur in our own time within the genus Drosera.

The long-leaved sundew is easy to cultivate, and plant material is available from different parts of its distribution area – both from the temperate zone and from the tropical Hawaiian population. The latter must be cultivated as a tropical plant that grows year-round. However, it tolerates down to 7 °C for a shorter period, as long as it does not experience frost.

I cultivate the long-leaved sundew outdoors, either in pots or in bog beds. It thrives in moist to wet conditions.

It is easy from seed, and the plants flower in their third year. There is variation in color and size among plants from different parts of the distribution, and some of them can turn completely red.

The plant forms a large winter bud during the winter.

Drosera brevifolia – Dwarf Sundew

This species is a small annual plant with a large distribution area from the southern United States south through Central America to Brazil. Its typical habitats are savannas, where the soil dries out in summer. Here it survives as seed, which germinates when the rains return in late summer. The plants grow through the winter and set flowers and seed when the summer heat arrives.

It forms a small rosette, typically 3–4 cm in diameter.

It reproduces by seed, which generally germinates poorly, and it is considered difficult in cultivation. I have never had success with it.

It does not tolerate much frost and is the least suitable, of the species described here, for cultivation under Danish conditions.

It does not form a winter bud.

Drosera capillaris – Pink Sundew

The pink sundew forms a rosette with leaves that lie flat on the ground. The leaf blades are round, and as a young plant it can resemble the round-leaved sundew (Drosera rotundifolia), which, however, most often has leaf blades that are broader than long. In contrast to this species, the pink sundew does not form a winter bud.

The flower is pink or white and sits on a flower stalk between 10 and 30 cm, depending on ecotype and local conditions.

It is distributed from Virginia in the north, through Florida and along all the coastal states of the southern USA. From here its distribution continues through Central America, Cuba, and far south in South America along the coasts.

It is easy to start from seed, which does not require stratification, and germinates in a combination of moisture, warmth, and light. My plants are kept moist but not wet.

Especially the forms from Alabama are quite hardy and thrive in an unheated greenhouse. All forms are, however, relatively short-lived and rarely survive beyond seed production.

In general, the species tends to spread uncontrollably throughout one’s plant collection, and it can be difficult to keep several populations separated under the same roof.

The hardiest forms do not tolerate much below –8 °C, but if it gets really cold and the plant dies, it quickly returns from seed, flowering the same year it germinates, or at the latest the following year. Over time, natural selection occurs, giving rise to more frost-tolerant plants.

It does not form a winter bud.

There are a number of variations within this species, and in cultivation, besides the standard form, we have two others that differ from the general appearance:

• An anthocyanin-free form. This lacks the red pigment, and the plants remain green regardless of how much light they receive. This form originates from Florida. The traits are genetically stable.

• The long-arm form. As the name suggests, this has long “arms.” The petioles are long, and in contrast to the normal form, the leaves are held above the ground. It resembles something between D. capillaris and D. intermedia, and may be a natural, fertile hybrid between them, though this has not yet been clarified. I maintain a form from Florida with long arms, and it is easy in cultivation but does not tolerate much frost.

Drosera filiformis – Thread-leaved Sundew

This is one of the most spectacular, winter-hardy species that we can grow from North America.

It is found only in the USA and Canada and is distributed in four separate areas along the east coast.
The northernmost area is Nova Scotia, where it occurs in five populations. The next area is Massachusetts, New York, and New Jersey. The third is North Carolina, and the last and southernmost is Florida.

The population in Florida is taxonomically separated from the others and has the status of a variety with the name Drosera filiformis var. floridana.

The plants form rosettes of long, very narrow leaves. The petioles are up to 1.6 cm long, and the leaf blade itself is between 20 and 30 cm. The leaves can range from green to red. As they grow, they unroll in the same way as fern fronds.

The inflorescence is typically 6–7 cm taller than the leaves and bears pink flowers with petals up to 1.2 cm long. The flowers are very attractive in July and August, lighting up every morning in dry or sunny weather. The plants set plenty of seed and are capable of both self- and cross-pollination. The large flowers are also frequently visited by insects. It is easy to propagate from seed or by division.

The plant forms a large winter bud.

The plants are very effective at catching low-flying insects up to crane fly size, but are usually covered with small insects. Stronger insects such as bees and wasps are not caught. The leaves show no snap movements, as many of the smaller species do.

Thread-leaved sundews from the three northern distribution areas are fully hardy in Denmark and can easily be grown in the garden or greenhouse, in moist, wet, or even shallow water. There is no advantage in greenhouse cultivation compared to garden cultivation, unless one wants to make controlled crosses to promote new flower colors.

The variety Drosera filiformis var. floridana requires protected greenhouse cultivation and does not tolerate much frost. There are, however, hardier selections that can withstand a fair amount of cold. Both subspecies form a solid winter bud. It has red to red-orange leaves and pink or white flowers. In every respect it is a smaller plant than the nominate form.

Thread-leaved sundew has a very large distribution, and plant material from across its range is in cultivation. The Canadian forms are generally much smaller than the more southern ones.

Selected forms include:

• Drosera filiformis filiformis f. viridis. An anthocyanin-free form with green leaves and white flowers. Genetically it originates from New Jersey and is fully hardy.

• Drosera filiformis filiformis f. rubriflora. A deeply pink/red-flowered form. A hardy type from New Jersey.

• Drosera filiformis filiformis “Pink flowers” from Nova Scotia. Smaller, slightly darker flowers, very beautiful. Somewhat shorter leaves than the more southern forms. Fully hardy.

• Drosera filiformis filiformis “False Vivipary.” This short-leaved Canadian clone forms small plantlets in the inflorescence instead of flowers. These do not appear to be usable for propagation. The color of the petals is unknown, since it does not produce true flowers. Hardy.

Drosera intermedia – Oblong-leaved Sundew

The oblong-leaved sundew is widespread in Denmark, but one must know where to look for it. Its habitat is often covered by water during winter, and on the nearly bare substrate left behind by summer drying, we find D. intermedia. In many places it grows in shallow water and can form stems up to 10 cm tall, so that the upper leaves still reach above the surface to breathe and catch insects.

Large prey is often found on the plants, and it is not unusual to see dragonflies and damselflies trapped.

Like the long-leaved sundew, D. intermedia has a very wide distribution, ranging from Europe across Canada and the USA, south through Cuba into northern South America. The tropical forms grow year-round, while the northern forms produce a winter bud and go into deep winter dormancy.

In the southern USA there is a great diversity within D. intermedia, and plants with stems up to 20 cm long are especially impressive. Similar to the Danish aquatic forms, it seems that stems only develop when plants grow in shallow, warm water, while the same plants cultivated on land form ordinary, low rosettes.

I have experimented with plants from across the species’ distribution in shallow water in the greenhouse during summer, and not all forms are able to form stems, even under identical growth conditions. There is clearly more to stem formation than the combination of water + warmth.

D. intermedia is an easy and beautiful plant that, in bog beds, will spread to the wettest areas, often covered with water in winter. It produces abundant quantities of highly viable seed, which prefers bare peat for germination. The species performs poorly in living sphagnum.

When cultivating the tropical forms, they require artificial light in winter as well as warmth. In the frost-free period in the greenhouse under natural daylight and variable day length, some tropical forms may develop a winter bud in autumn, like their more northern relatives from the temperate zone. However, they continue to produce leaves.

This may be a genetic remnant triggered by the shortened day length. It does not make them frost-tolerant, and they resume growth once moved into warmth. Not all tropical forms are able to form a winter bud. Perhaps this hidden ability says something about the species’ and the individual populations’ migration routes further south.

Many forms of this species are in cultivation, and in addition to several tropical types from Venezuela, Brazil, and Cuba, one often encounters:

• Drosera intermedia ‘Carolina Giant’. The American form from somewhere in the Carolinas is not particularly giant, but resembles a slightly more robust version of Danish plants. It can form stems over 10 cm if it grows in water. Fully hardy.

• Drosera intermedia ‘Anthocyanin free’. This completely green plant from North Carolina is fully hardy and can also form stems.

Drosera linearis 

This is a northern species whose distribution stretches from Nova Scotia to British Columbia. It is especially abundant in areas around the Great Lakes in the USA and Canada. Its northern range reaches as far as the Northwest Territories in Canada and south to Michigan, Wisconsin, and Montana.

The plant has narrow leaves. The leaf blade is between 3 and 7 cm long on a 2–4 cm petiole. The flower stalk is 5–12 cm tall. It forms a distinct winter bud.

In the wild it often grows on calcareous substrates but can also be found in living sphagnum together with the round-leaved and long-leaved sundews.

If one searches the literature for information on cultivation of this species, one will quickly conclude that it is almost impossible to grow, requiring a very cold, stable winter such as those found in northern continental climates, and that it has a short growing season.

Many solutions have been devised, involving freezers, special growth chambers, and other constructions. People who grow carnivorous plants are often very innovative.

It should be taken into account that much of the literature on D. linearis is written by growers who live further south than Denmark. I would recommend not reading about how to cultivate it, but simply trying it in a bog bed or in a pot outdoors.

Under Danish conditions it appears to be cultivable under exactly the same conditions as our native species, even with a relatively mild Danish winter, with long periods of fluctuating weather alternating between frost and thaw. Its growing season is no shorter than other northern species.

My guess is that it requires distinct seasons, most of all marked by clear variations in day length between summer and winter. Living this far north, we meet the plant’s requirements.

D. linearis can be grown from fresh seed, but it can be difficult to obtain it fresh, as so few growers succeed with it, and it seems to lose viability quickly. Seeds must be sown immediately after harvest or receipt, in an unheated greenhouse, and they germinate either the following spring or not at all.

Drosera rotundifolia - The round-leaved sundew

This native sundew, like our two other sundew species, belongs to some of the most widespread carnivorous plants in the world.

Here at home it is the most common sundew, but its total distribution covers all provinces of Canada, the northern USA south to Alabama, Mississippi, and California, Greenland, Iceland, the British Isles, Scandinavia south through Europe to Spain, Italy, Greece, Turkey, northwestern Russia, Belarus, Ukraine, Georgia, Mongolia, parts of China, Siberia, North and South Korea, and Japan.

In addition, there are isolated southern occurrences in Lebanon, the Philippines, and New Guinea. The latter two are entirely tropical populations which, like D. anglica in Hawaii or D. intermedia in South America or Cuba, grow year-round.

The leaf blade is between 1 and 2 cm, oval and broader than long. This becomes more pronounced the larger the leaf. The petiole is up to 2 cm. Occasionally, much larger plants occur with a diameter of up to 10 cm or more. The flower is small and white, borne on a scape up to 20 cm tall. It forms a distinct winter bud.

Here at home it is found in living sphagnum, both in full sun and in partial shade. It may also be found on bare peat and in moist depressions on heathland, where it can grow in what appears to be dry sand but turns out to be moist beneath the surface.

It is our most common carnivorous plant and is just as threatened as its habitats.

It has a great ability to spread explosively on bare soil, for example at Syvårssøerne south of Billund, where the lakes do not hold water every year, and on the moist, bare sandy bottoms one can in favorable years find tens of thousands of round-leaved sundews. In the years when the lakes return, they retreat to refuges along the shoreline.

The species has an enormous range, and one would expect great variation among plants from different localities. However, this is not the case, as the species is relatively constant in appearance across its range, with a few exceptions from Japan.

The major variations are often environmentally determined, and plants growing in living sphagnum, in sand, or in shade, look very different in size. But if moved to another environment, they change in appearance. The species is very plastic in its morphology and has a great ability to colonize relatively different types of habitats.

It is easy to cultivate outdoors in Denmark, and representative material from across the species’ range is in cultivation. For ordinary garden cultivation in Denmark, most forms can be recommended, as they are all essentially the same.

In Japan there exists a bright green form, free of anthocyanins. It is very small and more heat-demanding than the more northern forms, but it can thrive outdoors in a sheltered place and also does very well in an unheated greenhouse. It has poor seed production, but the seeds germinate readily.

From Japan another divergent form is known, which, like D. intermedia, produces long stems. This form is still hardly in cultivation.

It should finally be mentioned that, again in Japan, forms with pink flowers exist. To my knowledge these are not in cultivation.

The round-leaved sundew is easy from seed, which requires a cold winter to germinate.

Drosera tracyi 

This large sundew is distributed along the Gulf Coast of the USA in Mississippi, Alabama, Florida, and Georgia.

It is closely related to Drosera filiformis and was until recently regarded as a variety of that species. It differs from D. filiformis by having green to pale-green leaves and by its size. Drosera tracyi has leaves between 30 and 50 cm long. The tentacles of D. tracyi are short, which gives the leaves a compact appearance; on the other hand, the flowers are larger, up to 4 cm in diameter. These are borne on flower stalks up to 60 cm tall.

The giant thread-leaved sundew forms very large winter buds, even though it does not encounter much frost in nature.

The species is one of the few sundews that does not readily self-pollinate. If one has several clones of D. tracyi, it produces large amounts of seed with assisted cross-pollination, and it also easily cross-pollinates with D. filiformis.

The seed germinates easily when less than a year old and does not require stratification.

The giant thread-leaved sundew can be grown outdoors in summer but does not tolerate enough frost to overwinter outside, except in very mild areas of Denmark. It thrives in an unheated greenhouse down to –10 °C and benefits greatly from the longer and warmer growing season a greenhouse can provide.

It is a large and very beautiful plant. Various clones are in cultivation, both with and without locality data. These often differ slightly in appearance and in the shade of pink in the flowers.

From Alabama, an anthocyanin-free form has been brought into cultivation, called ‘Schnell’s White’. It has large white flowers. Since the giant thread-leaved sundew always has completely green leaves, it can be difficult to see whether it is a normal or an anthocyanin-free form. This can usually only be determined when it flowers.

Hybrids and Selections

When different sundew species meet in nature, hybrids often arise.

A number of these hybrids were originally described as wild species based on material found in nature and were given scientific names. Today, this practice is continued: an “×” is written after the genus name and before the species name to indicate that it is a hybrid.

In some places it is the practice to write “×” if it is a sterile hybrid, and without “×” if it is fertile. The long-leaved sundew is regarded as a fertile hybrid species, and therefore we write Drosera anglica. In nature, however, the round-leaved and linear-leaved sundews still cross, and these crosses, which are identical in appearance to D. anglica but sterile, may therefore be called Drosera × anglica. This is not accepted practice everywhere, and for the sake of simplicity I use “×” for all the following hybrids, fertile or not.

Since almost all species have been combined in hybrids, either in nature or in cultivation, it would be too extensive to go through them all here. But the most important ones must be included, as they make good garden plants.

Hybrids are, as mentioned, sterile and therefore do not produce viable seed. They compensate for this by growing vigorously and being easy to divide. In appearance, primary hybrids are intermediate forms between the parent species.

Drosera × californica – ‘California Sunset’

(D. filiformis filiformis × D. tracyi)

This hybrid was created in cultivation back in 1973 between D. tracyi and D. filiformis filiformis. It is in every respect larger than D. filiformis and, in contrast to D. tracyi, winter-hardy outdoors. It sets seed with cross-pollination, and I am currently producing new generations of it, which appear to be quite variable in size.

Drosera × californica arenaria

(D. filiformis floridana × D. tracyi)

This is the official name for the natural hybrid between the two species where they meet in Florida. In contrast to ‘California Sunset’, which involves the northern D. filiformis, this natural hybrid only involves less hardy parents, as the subspecies Drosera filiformis floridana is included.

I myself cultivate locality material from Florida, and fortunately the combination of the two species provides winter-hardy plants suitable for Danish conditions. Like the previous hybrid, it is a somewhat larger version of D. filiformis, with lighter leaves and larger pink flowers. It rarely produces seed but is easy to propagate by division.

Drosera × eloisiana

(D. intermedia × D. rotundifolia)

In the past this hybrid was called D. × belezeana, but the basis for the description of that combination turned out to be based on misidentified herbarium material. The name D. × eloisiana is therefore of more recent date.

The parent species often grow together, but the hybrid between them is very rare in Europe. Best known is the population in Dorset, southern England, and most cultivated material in Europe originates from this population. Here it forms large, dense clumps that propagate by division. The flowers are small and white.

I have seen a photo of Danish D. × eloisiana but have not visited the site myself. I have examined countless places in Denmark where the two species grow closely together, without finding it. In the USA it is more widespread across the area where the two species occur together.

The cultivar ‘Nightmare’ is a D. × eloisiana collected in Ocean Co., New Jersey. This is widely grown and is a good garden plant under Danish conditions.

There also exists a fertile form, which arose in cultivation and can be propagated from seed.

Drosera × hybrida

(D. filiformis × D. intermedia)

This widely cultivated plant was found in New Jersey. The material grown today mainly comes from a collection at Lake Absegami in Bass River State Forest in 1974.

D. × hybrida resembles a compact, miniature version of D. filiformis, with leaves about 9 cm long and narrow. The inflorescence reaches up to 17 cm, and the flowers are white or faintly pink.

In 1980 an unauthorized planting of D. × hybrida was made in Butterfly Valley, California. These were quickly removed again when concern arose that they might disturb the ecosystem. Some of this material, which had been outdoors, was later cultivated. Even though the material almost certainly all came from the sterile population at Lake Absegami, it turned out that some plants had become fertile. Along the way a mutation had occurred, and had they not been removed quickly, they could have established themselves as a new fertile species.

D. × hybrida is a good garden plant.

Drosera × obovata – Hybrid Sundew

(D. anglica × D. rotundifolia)

This hybrid arises almost every time these two species grow together in nature. This is also the case in Denmark, and at the few sites where we still have long-leaved sundew, we find the natural hybrid with the round-leaved sundew. The hybrid is also in cultivation and looks like a more robust intermediate form between the parents.

It is an easy plant that can be grown outdoors. Several clones exist in cultivation, though they do not differ much from one another. As with other hybrids, it is in principle sterile, but a fertile form has arisen in cultivation.