Drosera capensis (), the Cape sundew, is a perennial rosette-forming carnivorous herb in the flowering plant family Droseraceae. It is native to the Cape region of South Africa, where it grows in permanently wet, nutrient-poor habitats. Its elongated, roughly oblong leaves are held semi-erect and have a distinct petiole. It is quite a variable plant with several recognised growth forms, some of which form a short stem. As in all sundews, the leaves are covered in stalked glands that secrete sticky mucilage. These attract, trap, and digest arthropod prey, obtaining nutrients that supplement intake from the substrate in which the plant grows. D. capensis has dramatically mobile leaves that curl around captured prey, preventing its escape and facilitating digestion.
First recorded in the late 17th century, D. capensis was one of the five Drosera species included in the first edition of Carl Linnaeus' Species plantarum. A relatively large, 'showy' species that flowers readily and is considered very easy to grow, it was cultivated in Europe as a curiosity from the mid-18th century and is now one of the most widely-grown sundews. It has also been extensively studied, including as a potential source of bioactive compounds of pharmacological interest, and was the first sundew to undergo whole-genome sequencing. Although often uncommon and localised in its native range, it has become naturalised in several countries following deliberate introductions, and is listed as an invasive species in New Zealand.
Characteristics
Habit
D. capensis is a perennial herb forming a rosette typically in diameter, although occasionally up to . Its narrow, oblong leaves are held semi-erect. In summer, the plant produces one or two relatively tall inflorescences, each with between 15 and 30 flowers. The petals are typically pale purple.
Growth forms
D. capensis is quite variable across its range and several distinct forms have been informally identified.
Peter D'Amato described four forms in his 1998 book The Savage Garden: Cultivating Carnivorous Plants:
- D. capensis "Typical" with red-tentacled leaves long, and forming a scrambling stem
- D. capensis "Narrow" with narrow leaves and less tendency to form a stem
- D. capensis "Alba" similar to the "Narrow" form but with white flowers and pale tentacles
- D. capensis "Red" similar to the "Narrow" form but entirely reddish-maroon in colour when growing in bright light, with deep pink flowers
Robert Gibson noted the difficulty of assigning unlabelled plants to any of the informally described forms, due to short descriptions and the plants' variation in response to growing conditions. He detailed nine different forms: although in some growth forms it may be significantly longer.
Drosera species exhibit numerous different types of glandular trichomes (hairs). In addition to the large 'tentacles' involved in prey capture, leaves of D. capensis have two types of microscopic glandular trichomes: 'Type 3' trichomes (short, unbranched, biseriate, stalk two- or three-celled, gland vertically divided) and 'Type 10' trichomes (unbranched short glandular hairs, stalk biseriate, gland multicellular).
Movement and prey capture
thumb|alt=A fly is captured by the leaf of Drosera capensis; first the tentacles near the fly bend toward it, then the whole leaf enfolds the fly |Time-lapse video of Drosera capensis leaf movement following prey capture
Like all sundews, D. capensis attracts, captures and digests prey by means of stalked glandular trichomes ('hairs' or 'tentacles') that secrete droplets of sticky mucilage containing digestive enzymes. When a potential prey item contacts the marginal tentacles, they bend toward the centre of the leaf, bringing the prey item into contact with more tentacles. Adjacent marginal tentacles also move toward the prey, making it more difficult for the prey to escape and facilitating digestion.
D. capensis is among the sundew species in which the lamina itself also exhibits significant movement. When prey is detected, the leaf blade will slowly bend inwards around the location of the prey, enfolding it. In D. capensis the leaf can bend through more than 180 degrees, 'rolling' around the prey. The extent to which the leaf bends depends on the location of the prey; the closer the prey to the tip of the leaf, the more pronounced the bending response.
Experiments involving treatment of leaves of D. capensis with an auxin (indole-3-acetic acid, IAA) and an auxin transport inhibitor (2,3,5-triiodobenzoic acid, TIBA) demonstrated that bending of the leaf is caused by a hormonal growth stimulus transported from the tip of the leaf to the bending point, and induced by a signal originating at the location of the prey.
Flowers and seeds
alt=An inflorescence on a thin stem with two spent flowers, one open pink flower, and a curling row of unopened flower buds|thumb|Inflorescence of Drosera capensis
The plant produces one, two or occasionally three inflorescences, The pedicels are semi-erect and long. Sepals are obovate, long and wide, and usually green. D. capensis contains the naphthoquinone ramentaceone (7-methyljuglone) and trace amounts of plumbagin (its isomer). These compounds have antifeedant, allelopathic and antimicrobial properties and are believed to play a defensive role in plants. They are also of interest for their potential medical uses, including antibacterial and anti-cancer applications.
D. capensis contains the flavonoids myricetin and quercetin, which are also of pharmacological interest. The species has been the subject of studies aiming to increase the biosynthesis of its naphthoquinones and flavonoids by applying elicitors including jasmonates and Agrobacterium rhizogenes,
The red-leaved form of the species was the first sundew—and the first carnivorous plant from order Caryophyllales, which also includes Nepenthes, Aldrovanda, Drosophyllum and Dionaea—to undergo whole-genome sequencing. The genome spans a total of 264 Mbp. Despite its reputation as a weed in cultivation, but his plan for a detailed publication on African plants was not fulfilled prior to his death in 1695 A plant that could be D. capensis is listed among the four types of Ros Solis (sundew) in this work, described as Ros Solis Africanus, folio lato, & longo (African sundew, broad and long leaf).
The third volume of John Ray's Historia Plantarum, published in 1704, included descriptions of three African Ros Solis, which were attributed to William Sherard. Among these is Ros Solis Africanus, foliis praelongis, caule nudo altissimo (African sundew, very long leaves, very tall bare stem).
In 1880, the same journal published an illustrated note on D. capensis and D. spatulata by Édouard Morren, recommending these Drosera species as "among the most interesting and easiest to cultivate". The note provided detailed cultivation information, including observations that the plants require pure water and are calcifuges. The illustrations were based on plants grown in greenhouses where they had "thrived for several years, multiplying, and flowering regularly". Morren described cultivation of the plants in the coolest part of a hothouse, where they were watered via drops of condensation from the roof.
alt=Refer to caption|thumb|Colour illustration of Drosera capensis from [[Curtis's Botanical Magazine, 1881]]
The plant was illustrated by Matilda Smith in Curtis's Botanical Magazine in 1881, along with a description by Joseph Dalton Hooker noting that it had flowered in July in a cool greenhouse at Kew.
In Carl Georg Oscar Drude's 1888 treatment of Droseraceae, D. capensis was given as one of the example species within subg. Ros-solis section Vagae.
20th century
In 1906, the first true monograph of Droseraceae was published in Das Pflanzenreich by German botanist and collector Ludwig Diels.
Cultivation
D. capensis is one of the most widely cultivated sundews.
Growing conditions
The plant requires warm-temperate conditions and is often grown as a houseplant (on a windowsill or in a terrarium), in a greenhouse, or outside in areas with suitable climate.
{| border="2" class="wikitable"
|+ Cultivars of Drosera capensis
! Cultivar !! Description
|-
|Drosera 'Albino' <small>Hort. Borret & Farrow</small>
|White flowers, lack of red colouration in the leaves and tentacles
|-
|Drosera 'Narrow Leaf' <small>Hort. D'Amato</small>
|Similar to "typical form" but with narrow lamina and petiole, and more compact, rarely producing a tall stem
|}
Drosera 'Albino' and Drosera 'Narrow Leaf' have both received the Award of Garden Merit from the Royal Horticultural Society.
The following Drosera hybrid cultivars with D. capensis involvement are listed by the ICPS:
{| border="2" class="wikitable"
|+ Hybrid cultivars involving Drosera capensis
! Cultivar !! Parentage !! Description
|-
|Drosera 'Anemone' <small>Hort. H.Carlton</small>
|D. oblanceolata × spatulata × capensis
|Stout rosetted plant with elongate leaves intermediate between 'paddle-shaped' and 'strap-shaped'; very tall inflorescence with pale pink flowers
|-
|Drosera 'Hercules' <small>Hort. C.Trexler</small>
|D. capensis × aliciae
|Similar in habit to D. capensis but with strikingly broadened leaves that barely reflex, and a tendency to form clumps
|}
Conservation status
, Drosera capensis does not have an assessment on the IUCN Red List. On the South African National Biodiversity Institute's Red List of South African Plants it is listed as 'Least Concern', a categorisation applied automatically because it was not highlighted in screening processes used to select taxa of potential conservation concern for detailed assessment. In 2020, as part of a large-scale conservation status assessment of carnivorous plants, it was assessed using IUCN criteria as 'Least Concern'. Many of these locations are ecologically sensitive, and introduced species such as D. capensis may compete with threatened local flora. It has become established in the Waitākere Ranges, either due to deliberate planting or via soil contamination from other introduced plants. Its seeds are believed to be distributed by waterfowl. The species is subject to 'sustained control' under the Conservation Auckland Regional Pest Management Plan.
In Mendocino County California, Albion Bog—a raised bog in rare dwarf forest habitat—has become infested with non-native carnivorous plants as a result of deliberate plantings by enthusiasts from the 1960s onwards. Drosera capensis has formed dense stands, outcompeting the native sundew D. rotundifolia, and conservationists have found it impossible to eradicate.
In Australia, D. capensis was reported as naturalised at a single site in the Royal National Park, where at least 100 adult plants were observed.
In Hawaiʻi, although not known to be naturalised, it is assessed as a 'high risk' species by the Plant Pono initiative due to characteristics including its self-fertility; prolific seed production; capacity for hybridisation; rapid growth to maturity; tolerance of a wide range of growing conditions; and ability to regenerate after frost and fire damage.
The species is listed (with a 'low' risk rating) in A Global Compendium of Weeds.