Drosera capensis

Strap leaves on a short woody stem

Drosera capensis is an evergreen perennial, usually about 15 cm tall, with leaves radiating from a short, woody stem that creeps below ground as a rhizome ^[2]. Each leaf has a stalk (petiole) about as long and wide as the sticky blade above it. The New South Wales flora gives the blade as linear, up to 35 mm long and occasionally 65 mm, and about 4 mm wide ^[4]. Tentacles crowd along the margins and are fewer and shorter in the center, while the underside of the leaf is smooth ^[2].

The flower stalk grows up to about 30 cm and carries 15 to 30 pink-mauve flowers with petals 10 to 15 mm long. They open from the bottom up, one or occasionally two at a time. The seeds are black, spindle-shaped and about 0.8 mm long ^{[4, 2]}.

Among Australian and garden sundews it is easy to separate. The PlantNET key distinguishes it from D. binata by its unforked leaves, and from D. arcturi by its many-flowered stalk; the same key notes that dark pink and white cultivars are available ^[10].

A slow but selective trap

The trap works in stages. In a 1983 Carnivorous Plant Newsletter photo series, an anesthetized fruit fly placed at the edge of a leaf was coated in mucilage and moved inward within an hour; over five hours the bending tentacles carried it from the side of the blade to the center, and the marginal tentacles bent over it as well ^[11]. Larger prey can also be wrapped as the leaf blade folds over ^[2].

Laboratory work on this species has explained how the plant decides whether to digest. In a 2017 study, touch and live prey caused fast, local tentacle bending and enzyme release where the stimulus was applied, but the traps needed chemical signals from the prey to reach full digestive activity ^[12]. A 2023 follow-up tested Charles Darwin’s observation that sundew tentacles do not respond to a drop of water. Drops of water triggered the fewest electrical signals, did not raise jasmonate hormone levels and did not switch on the digestive enzyme droserasin, while ammonia, chitin, touch and insects all did ^[13].

In the wild and outside it

The Cape sundew is native to the southwestern Cape, where it grows in marshes, along streams, in permanent seeps and in damp fynbos ^[2]. South Africa’s Red List treats it as a national endemic of the Western and Eastern Cape with a stable population ^[3]. In habitat it flowers in December and January. Each flower opens for only a few hours in good sunlight and is usually self-pollinated, and the light seeds fall close to the parent ^[2].

It has also turned up outside its range. In 2012 botanists reported it as a new naturalized plant for Australia: a colony of at least a hundred adults on a 5 m stretch of creek in Royal National Park, growing among native D. spatulata, D. binata and bladderworts, with profuse flowering and seed ^{[4, 6]}. Control measures to eradicate it were under way ^[6]. ICPS regards releasing plants into the wild as unethical ^[14], so keep seedlings and discarded plants out of natural wetlands.

Growing it

The ICPS guide to subtropical sundews, which covers the rosetted species of southern Africa and other warm regions, sets out the general rules: no dormancy, a comfortable range of 10 to 35 °C (50 to 95 °F), and soil anywhere from pure sphagnum to peat:sand mixes, without fertilizer ^[7]. PlantZAfrica, from the botanic garden at Kirstenbosch, calls it one of the hardiest carnivorous plants to grow and recommends equal parts sand and peat in a 10 to 15 cm pot standing in 1 to 3 cm of water ^[2].

The sources disagree on light. PlantZAfrica treats the Cape sundew as a house plant for a sunny window ^[2]. ICPS says subtropical sundews want more light than a windowsill provides and recommends 15,000 to 25,000 lux, 12 to 16 hours a day, for most Drosera under lights ^{[7, 8]}. ICPS adds that plants survive with less light but do not grow as well ^[8]; see light for carnivorous plants and sundew not making dew. The plant can also take more cold than the subtropical label suggests. A grower writing for ICPS lists it among the plants that succeeded outdoors all year in Pacific Northwest bog gardens, and in one bog near Portland, Oregon, it took over the space around the flytraps ^[15].

PlantZAfrica names aphids, mealybugs and thrips as the main pests and warns against soap-based insecticides ^[2]; see aphids, mealybugs and scale. Dew may stop for a while after repotting or handling, and new leaves bring it back ^[2]. Where prey is scarce, ICPS suggests rehydrated dried bloodworms placed only on dewy leaves ^[7].

Registered forms

Two cultivars of the species itself are registered with ICPS ^[16]:

• ‘Albino’: white flowers, and no red in leaves or tentacles even in strong sun. It came true from seed when first described in 1989.
• ‘Narrow Leaf’: narrow leaves and petioles, with tall stems rarely produced, so the plant stays compact.

ICPS also lists hybrids with D. aliciae, such as ‘Caprice’ ^[16].

Propagation

Seed is the simplest route. Sow it on the surface of a moist mix without covering it ^[2]. ICPS germinates subtropical sundew seed at 20 to 25 °C (70 to 80 °F), where it sprouts in a few weeks ^[7]. Cape sundew seedlings first show non-carnivorous seed leaves (cotyledons) before the sticky true leaves ^[9]. Leaf and root cuttings also work ^[2]. ICPS floats leaf pieces, tentacle side up, in pure water in a closed jar ^[17]; the sundew leaf cuttings guide and sowing seeds give step-by-step methods.