Saturday, 9 July 2011

Something different: the Sundews

 This week I thought I would take a break from talking about animals and instead write about one of their more unusual predators. I grow a small collection of carnivorous plants and last week at Chester Zoo there was an international meeting of growers from all over Europe. As well as plants for sale, there were also great displays, including from the national collections of Sarracenia and Drosera, and I came away with three of the latter for my collection.

Sundews have figured in folklore from early times, as it was recognised that instead of dew disappearing with sunshine, on these plants it actually increased, which was thought to be magical. Of course, what people were seeing was not dew drops but sticky mucilage on short tentacles that cover the leaves, and which trap insects, usually small ones. These are digested by enzymes secreted by the plant, giving it a boost of nitrogen lyand phosphorous that cannot be obtained from the soil it grows in, typically sphagnum bogs and other nutrient-poor soils. Mostly these habitats are constantly wet, but some Australian sundews live in areas where the swamp dries out, and these survive the dry season as small tubers deep in the sandy soil.

The insect-eating habit is plainly very ancient, as most insectivorous plants can be placed in a clade closely related to Drosera, even if they have totally different trapping mechanisms, such as the Southeast Asian Nepenthes species. Drosera species can be found in their characteristic swamps all over the world, but the largest diversity of species is in Australia, with South Africa close behind.

As flowering plants, carnivorous plants have an obvious problem – how do they avoid killing the insects that pollinate their flowers? The answer lies in the specialised targeting of their trapping leaves, which usually focus on a small range of flying insects, especially mosquitoes. The flowers, which are usually pink or white and quite attractive, are carried on tall stalks and are pollinated by different insects. If no suitable pollinators arrive, the flowers are usually also self fertile. The tiny black seeds are dispersed by the wind and can germinate wherever suitable habitat can be found, although this is usually close to the parent plant.

Unfortunately, although Bristol Zoo has quite a good carnivorous plant collection, they do not currently have a suitable display area, so the plants mostly stay in off-show greenhouses. As a group, many carnivorous plants are much easier to grow than people think, as long as their key requirements are met. The most important of these is water, which must be mineral-free, preferable rainwater or reverse osmosis water. The plants should stand in this constantly in the summer, but in the winter when growth slows the pots should be kept damp only. The growing medium needs to be acidic – a standard mix is of peat+perlite, but sand may also be added. If a peat substitute is used, it is important that the PH of the medium be tested and should be kept acidic. The final need is light – most Droseras, and other carnivorous plants, are exposed to full sun in the wild and do not tolerate shade, so they do best in a greenhouse although a sunny windowsill will be adequate for most of the small forms, likely the widely available D.capensis which can be found in most garden centres.

Finally, here is some brief information about three species I got up at Chester:


This species is widespread in South Africa and Madagascar, and can grow up to 25cm tall. It tends to die back in the winter, but will regrow in the spring. As with most of the South African sundews, it is easy to grow, in the same was as D.capensis.

D.filiformis traceyi

This is a hardy North American species with a range from Canada all down the eastern sea board to Louisiana, and I currently have this outside in a water tray. As with many Droseras from temperate climates, it dies back to a resting bud called a hibernaculum in the autumn, sprouting again in the spring. There are two forms of this, one with red tentacles on the leaves and the form I have, var traceyi, which has white ones. The leaf form is very distinctive – 10cm or more long thread-like leaves, which unfurl from the base like a fern.


Originating from Australia, across to New Zealand and South East Asia, D.spathulata is as one might expect from so wide-ranging a plant quite variable. It generally forms rosettes about 4cm across, with a flower stalk about 6cm high. It can be a weed in carnivorous plant collections, as it produces large amounts of seed.

One final though for anyone interested – be careful about growing any carnivorous plant from seed bought in a seed store. The seeds of most carnivorous plants lose viability quickly, and the best way is to buy live plants or join a society like the UK Carnivorous Plants Society, as members receive as part of the membership an annual seed list of many unusual species produced by members, and which is therefore still fresh and viable.

For more information, check out the CPS forum at

(images from wikipedia)

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