| Cape sundew | |
|---|---|
| |
Scientific classification 
| |
| Kingdom: | Plantae |
| Clade: | Tracheophytes |
| Clade: | Angiosperms |
| Clade: | Eudicots |
| Order: | Caryophyllales |
| Family: | Droseraceae |
| Genus: | Drosera |
| Subgenus: | Drosera subg. Drosera |
| Section: | Drosera sect. Drosera |
| Species: | D. capensis
|
| Binomial name | |
| Drosera capensis | |
Drosera capensis, commonly known as the Cape sundew,[1][2] is a small rosette-forming carnivorous species of perennial[3] sundew native to the Cape in South Africa. Because of its size, easy-to-grow nature, and the copious amounts of seed it produces, it has become one of the most common sundews in cultivation, and thus, one of the most frequently introduced and naturalised invasive Drosera species.
D. capensis produces strap-like leaves, up to 3.5 centimetres (1.4 in) long (not including the petiole) and 0.5 centimetres (0.2 in) wide,[4] which, as in all sundews, are covered in brightly coloured tentacles which secrete a sticky mucilage that traps arthropods. It is a perennial, herbaceous plant that forms a rosette with a diameter of 18 to 25 cm (7.1 to 9.8 in) and is characterized by numerous, reddish glandular erosions on 7 cm (2.8 in) long and 5 mm (0.20 in) wide, elongated leaves.
The plant flowers in summer (December and January in its native habitat in South Africa) with up to fifty pale-violet, over 2-centimetre (0.79 in) large flowers, borne on up to 35 cm (14 in) high racemose inflorescences. The flowers can self-pollinate upon closing and produce copious quantities of very small, spindle-shaped seeds, which are released from the capsules that form when the flowers have died. The plant thrives in full sun locations on nutrient-poor, waterlogged and lime-free soils.
Drosera capture insects by luring them with their glossy, magenta-hued beads of false "nectar" (seen covering the tentacles of healthy leaves); this nectar is, of course, merely sticky droplets made-up of digestive enzymes. The secretions act as a visual attractant to nearby insects, as it shines in the sun (hence the common name of sundew). Furthermore, when Drosera plants come into bloom, the flowers themselves bring more potential prey to the vicinity of the plant.
At first, when a prey item such as an insect, is stuck to a Drosera leaf, it may find itself deeply trapped, right away, or only partly stuck (based on the angle of its initial landing); if not fully stuck, the movements of the prey trying to wriggle free will often trigger the leaf-tip to fold back onto itself to ensure the bug cannot escape. However, this does not always occur; the insect may simply remain stuck to (and ultimately digested on) an open leaf. The action itself is comparable to a person extending one arm outwards, and rolling their hand back, much like a "bicep curl". Not only does this action serve to further secure the sundew’s victim, but it allows for more leaf surface area (and thus, digestive enzymes) to come into contact with the prey, ensuring digestion. Once the prey is fully trapped, initial breakdown often begins within an hour; wriggling or attempting to escape will only trap the insect further. Digestion takes well-over six hours from the time of an insect's initial landing.
If a prey organism has been caught in the secretion of the tentacles, then the tentacles near the victim will bend towards it, until a portion of the tentacle-covered region of the leaf has wrapped around the animal. Secreted enzymes will digest the insect until only the chitin remains. The absorption of nutrients takes place via the tentacle tips, where the secretion itself is produced. When the prey item is decomposed enough that the plant cannot gain further nutrients, the leaf and the tentacles return to their original position.[5]
The sundew secretes mucin to trap its prey, which consists of a variety of species, including bees, small wasps, beetles; fruit flies such as Drosophila and Ceratitis capitata; Diptera, like fungus gnats and house flies; lacewings, and other arthropods. The plant may occasionally catch aphids or mealybugs, which are drawn to the sticky leaves, as they attempt to feed on the crown of the plant—Drosera are not immune to destructive sucking insects and other pests. The mucin is an approximately four-percent aqueous solution of an acidic polysaccharide, with a pH of around 4. The mucin secretions of Drosera capensis have a high viscosity; fresh mucin can be stretched into a thread up to a meter in length. This suggests that the mucin is predominantly composed of acidic polysaccharide; these polysaccharides interact extensively and are highly hydrated.[6]
Drosera capensis has two color-forms: red-tentacled and white-tentacled. It has been hypothesized that visual cues, such as tentacle coloration, could be a factor in prey attraction in carnivorous plants, in addition to the olfactory signals used. In prey-attractant experiments, Drosophila melanogaster fruit flies were introduced to the red- and white-colored forms of D. capensi in the laboratory. The D. melanogaster seemed to have no preference for color of plant tentacles, as there was no difference in the mean number of the flies captured between the two forms of the sundew. Coloration in D. capensis is due to anthocyanin pigment – or the lack of – and does not affect the ultraviolet (UV) coloration of the plant. It is the UV coloration which, along with olfactory signals, appears to important in attracting prey. Increased photosynthesis was observed in plants fed with fruit flies.[5]
In early summer or late spring, D. capensis produces multiple, small, five-petaled pink flowers at the end of scapes which can be up to 30 centimetres (1 ft) tall.[4] Flowers individually open in the morning and close by mid-afternoon, lasting just one day each with the next one up the scape opening the following day; the lower ones on the scape can thus be open or "past" while the ones at the top are still forming.
Under horticultural conditions, carnivorous plant enthusiasts find that these seeds have a tendency to find their way into neighbouring plant pots where they germinate readily, giving D. capensis a reputation as a weed.
Drosera capensis has several forms or varieties, including the "typical", "wide-leaved", "narrow-leaved" and "red" forms and the cultivar Drosera 'Albino'.[7] The typical form is noted for wider leaves and the gradual production of a scrambling stem as it grows. The "wide-leaved" form is similar to the "typical" variety, but produces leaves at least 50 percent wider than the typical variety. The narrow-leaved form differs from the typical form in that it rarely produces tall stems; has thinner, longer leaves and less hair on the plant. Drosera capensis 'Albino', is also similar in shape to the "typical" form, but lacks most of the red pigmentation of the typical or narrow forms, with clear or pink trichomes and white flowers. There is also the "red" form that turns blood red in full sunlight, and is also similar physically to the narrow-leaved form. These varieties are commercially available.[7]
Drosera capensis "narrow-leaved" has won the Royal Horticultural Society's Award of Garden Merit.[8]
Drosera capensis can be easily propagated through a variety of methods including seed, leaf cuttings, and root cuttings. It is not easily killed by temperature extremes of a short duration and is a generally forgiving plant to grow. Additionally, D. capensis does not undergo dormancy like some sundews. It is among the easiest of carnivorous plants to keep indoors. It grows very well in open air, on a sunny windowsill, as long as it is kept in an inch or two of mineral-free water.[7] It does not require a terrarium although it can benefit from one.
The ideal substrate is composed of 70 percent of blonde peat and 30 percent of non-calcareous sand. The ideal temperature varies between 5 and 15 °C (41 and 59 °F) in winter and between 20 and 40 °C (68 and 104 °F) in summer, for a hygrometry of 40 to 80 percent. Moist soil must be maintained year-round by the presence of a saucer under the pot, but watering must be reduced and the saucer removed in winter. High ambient humidity allows the preservation of mucilage. An exposure in full sun suits it perfectly, although a place a little less sunny may be suitable.
Drosera capensis is listed on the New Zealand National Pest Plant Accord due to it being classified as an invasive species in that country, where they cannot be bought at plant retailers and should not be traded by carnivorous plant partisans. They have been planted in the wild or unintentionally introduced through soil contaminated by seeds with plantings of pitcher plants and water lilies. They are now beginning to spread on their own, potentially with help from water birds.[9]
Drosera capensis have also been found in Australia. Currently it has only been found in New South Wales but understanding the species distribution is essential to managing the species in the future. It has also been found in the state of California and classified as a naturalized weed. Alongside Australia, California and New Zealand, Drosera capensis have also been found in peat bogs in South America.[10] It is currently classified as an invasive species.
