Roridula dentata is a tentacle-leaved shrub that has a unique symbiotic relationship with assassin bugs (Pameridea marlothii). Although commonly known as the flycatcher bush, this plant does not consume the insects it traps but rather provides food for its insect guest. It has been known to catch small birds.
Roridula dentata is a shrub up to 2 m high;, the leaves are lanceolate having margins with teeth and tentacles, and are covered with numerous sticky hairs, which are different lengths and covered with a gummy glue-like substance. The flowers are pink and are borne on the ends of hairy pedicles in the axils of the upper leaves. Flowering time is in spring (September to October) in the southern hemisphere. Plants do not live long and bush fires initiate seedling germination.
Roridula dentata is currently not listed on the South African Red Data List of 1996, however the Millennium Seed Bank team based at Kirstenbosch are working with the Threatened Species Programme (TSP) currently revising the Red Data List under IUCN guidelines. It has been noted that although this shrub had a wide distribution historically, many populations listed in herbaria are no longer in existence. This is due to too frequent fires, fires at the wrong season when seeds are germinating or habitat destruction by agriculture. With the data now at hand it is envisaged that Roridula dentata may be given a status of Vulnerable (VU) or even Endangered (EN). Although seed from this species is known to have an ample longevity in storage, the parent plant often does not produce large quantities of seed. Thus there is often insufficient seed for seed banking and also to regenerate the soil seed bank in situ.
The most devastating threat to R. dentata populations is agriculture, specifically the production of Rooibos tea which is one of the only crops that can be grown in the mountains of the Cape, in the same habitat as this species. Due to its unique relationship with an insect, it is not the only species that is rare or threatened, Pameridea marlothii, only occurs on Roridula dentata, a leggy insect that may hold the key to the growth and pollination of this perennial shrub.
Distribution and habitat
Found at altitudes of 900-1 200 m in the Cape Fold Mountains of Clanwilliam, Ceres and Tulbagh, it prefers moist, damp localities and is generally found in habitats such as bogs, marshes and on the banks of rivers. Although occurring in very moist habitats, the biome type is arid mountain Fynbos and annual temperatures average 27 ° C. The dry summer winds and low rainfall make this an extremely harsh environment to survive in, yet Roridula dentata is very tolerant of these conditions.
Derivation of name and historical aspects
Derived from the Latin words rorida (dewy; wet with dew) and dentata (toothed), as this species has wet, toothed leaves. The family Roridulaceae consists of the genus Roridula that has two species both endemic to the Cape Province of South Africa, R. gorgonis and R. dentata.
In spite of the fact that Roridula dentata has sticky insect-trapping liquids on its leaves like the Drosera species also of the Cape, this sap has no digestive enzymes to digest the prey. Numerous small bugs ( Pameridea, family Miridae) live on the plants and have specially adapted feet which enable them to run freely over the sticky sap.
Pameridea then roam the plant for insects, on finding a trapped insect, they probe the hapless victim with their proboscis, inject venom each time until the prey succumbs and dies.
They then defecate on the leaves of Roridula leaving nitrogen-rich faeces which act as fertilizer for the plant, which then absorbs it through its leaves. The assassin bugs occur nowhere else in the world and are thus also threatened. They need the plant to catch their food in order to mature and reproduce and the plant needs the juvenile bugs to pollinate the flowers whilst crawling around for food. It has also been noted that bees visit the flowers and allow pollination between different plants, without being caught. This symbiotic relationship allows for both the insect and plant to obtain food through the other's actions.
Growing Roridula dentata
This plant is best grown from seed and must be sown in April and May, as these months have hot daytime temperatures and cooler night temperatures. An ideal pot specimen, Roridula dentata should be kept in a warm sunny spot on a balcony or window sill. Unless you know an entomologist who could supply you with some assassin bugs the best is to feed your plant with a liquid fertilizer high in nitrogen. Treat the seeds with Kirstenbosch Smoke Primer and then sown into trays or pots containing equal parts milled pine bark (or palm peat) and medium river sand. Place the seeds on the surface of the medium and lightly cover with a layer of sand, don't plant them too deep. Germination can take up to three months, so don't throw out your medium after a couple of weeks if nothing has come up! Although this plant has a reputation for being hard to cultivate, with the correct care it can thrive, the main cause of plant loss is over-watering. As R. dentata occurs in an arid habitat (hot dry summers), it is recommended that you mist these plants with a fine spray during the summer months rather than drenching them with a watering can when they look dry.
References and further reading
- Leistner, O.A. (ed.). 2000. Seeds plants of southern Africa : families and genera. Strelitzia 10. National Botanical Institute, Pretoria.
- Reiner, M. 2003. Cultivation and description of Roridula gorgonias and Roridula dentata. www.drosophyllum.com
- Smith, C.A. 1966. Common names of South African plants. Memoirs of the Botanical Survey of South Africa No. 35.
- Website: The largest carnivorous plant grows on our doorstep. http://fernkloof.com/other.mv