Drosera regia, commonly known as the king sundew, is a carnivorous plant in the sundew genus Drosera that is endemic to a single valley in South Africa. Individual leaves can reach in length. It has many unusual relict characteristics not found in most other Drosera species, including woody rhizomes, operculate pollen, and the lack of circinate vernation in scape growth. All of these factors, combined with molecular data from phylogenetic analysis, contribute to the evidence that D. regia possesses some of the most ancient characteristics within the genus. Some of these are shared with the related Venus flytrap (Dionaea muscipula), which suggests a close evolutionary relationship.
The tentacle-covered leaves can capture large prey, such as beetles, moths, and butterflies. The tentacles of all Drosera species have special stalked glands on the leaf's upper surface that produce a sticky mucilage. The leaves are considered active flypaper traps that respond to captured prey by bending to surround it. In its native fynbos habitat, the plants compete for space with native marsh grasses and low evergreen shrubs. Of the two known populations of D. regia, the higher elevation site appears to be overgrown and is essentially extirpated. The lower elevation site is estimated to have about 50 mature plants, making it the most endangered Drosera species, since it is threatened with extinction in the wild. It is often cultivated by carnivorous plant enthusiasts, and a single cultivar has been registered.
Description
Drosera regia plants are fairly large herbs that produce horizontal woody rhizomes and a crown of large, linear leaves up to long and wide. The leaves possess stalked glands (tentacles) on the upper surface of the lamina along nearly the entire length of the leaf. The leaves lack petioles and stipules, emerging by circinate vernation (uncurling) and tapering to a filiform point. The tentacles and the leaf itself are capable of responding to prey by bending toward insects trapped in the sticky mucilage produced by the glands. Leaves are even capable of folding over themselves several times. Each leaf can possess thousands of tentacles, which can aid in the retention of larger prey when combined with the leaf wrapping tightly around captured insects. In its native habitat, D. regia has been known to capture large beetles, moths and butterflies. Plants go dormant during the colder season and form a dormant bud, consisting of a tight cluster of short, immature leaves. Plants begin to break dormancy in mid-July with a typical growing season lasting from October to April, though this is variable and plants can continue growing year-round without dormancy.Obermeyer, A. A. 1970. Droseraceae. In L. E. Codd, B. Winter, D. J. B. Killick, and H. B. Rycroft [eds.], Flora of South Africa, 13: 187–201. Department of Agricultural Technical Services, Pretoria, South Africa.McPherson, S. 2008. Glistening Carnivores: The Sticky-leaved Insect-eating Plants. Poole, Dorset, England: Redfern Natural History Productions. pp. 154–157. Individual leaves die back but remain attached to the short stem, clothing the bottom portion of the plant in the blackened dead leaves of former years.
The woody rhizomes produced by the plant are one of the unusual characteristics that it shares only with D. arcturi in the genus; the absence of woody rhizomes in all other Drosera is often cited as an indication of the presumed ancient lineage of D. regia and D. arcturi. Drosera regia also produces relatively few thick, fleshy roots, which possess root hairs along the terminal . Asexual reproduction of mature plants usually occurs after flowering with new plants arising from the rhizome and roots. After a fire, undamaged roots will often re-sprout new plants.
Drosera regia flowers in January and February, producing scapes up to long. The scapes emerge vertically, lacking the circinate vernation of its leaves and all other scapes of the genus Drosera, with the exception of D. arcturi. The scapes consist of two primary branches and bear 5 to 20 (sometimes 30) unscented pink flowers with long petals. Bracts are small, bearing some reduced tentacles. Each flower has three unbranched, spreading styles emerging from the top of the ovary and extending beyond the five erect stamens (15 mm long), which surround the ovary. This arrangement minimizes the chance of self-fertilisation. Studies have shown that the operculate pollen shed in tetrads (fused groups of four pollen grains), characteristics that are similar in the related Dionaea muscipula (the Venus flytrap) and Aldrovanda vesiculosa, is incompatible with clones, failing to produce seed when plants are self-fertilised. Seeds are brown to black, linear and ornamented with fine network-like markings, and 2 mm long and 0.5 mm in diameter. Seed is shed by the end of March.
The unusual characteristics that set it apart from other species in the genus include the woody rhizome, undivided styles, and the operculate pollen.Seine, R., and Barthlott, W. 1994. Some proposals on the infrageneric classification of Drosera L. Taxon, 43: 583–589. Drosera regia shares other features with the robust Tasmanian form of D. arcturi, including the lack of stipules and petioles and the non-circinate growth of the scape.
It has a diploid chromosome number of 2n = 34, which is unusual for the genus Drosera and closer to the diploid chromosome number of the Venus flytrap (Dionaea muscipula), another member of the Droseraceae. Variable chromosome counts for Dionaea from multiple studies include 2n = 30, 32, and 33. Of the Drosera species with known chromosome counts, most are a multiple of x = 10. Based on an extensive review of karyotype studies, the botanist Fernando Rivadavia suggested that the base chromosome number for the genus could be 2n = 20, a number that many Drosera species share including the widespread D. rotundifolia. Exceptions to this base number include the Australian, New Zealand and Southeast Asian Drosera, which have chromosome numbers ranging from 2n = 6 to 64.
Distribution and habitat Drosera regia is endemic to South Africa and has only ever been found at two sites at elevations of in the Bainskloof Range near Wellington, Western Cape in South Africa. Despite extensive exploration, D. regia has not been found at any similar location in neighbouring valleys. Small morphological variations such as broader leaves have been recorded from these two small populations, which are restricted to an area of just a few hundred square meters. Drosera regia is found in a natural fynbos vegetation amongst dense marshy grasses. The fynbos habitat is similar to a low or medium shrubland or heathland, dominated by low evergreen shrubs.
The lower elevation site where D. regia is found is characterised by permanently damp soils consisting mostly of a gravel bench formed from a creek bed. The plants grow in a peaty quartzite sand, often with a gravel cover. Rhizomes of mature plants grow above ground and among associated grasses and sedges when gravel is absent and below ground when there is a gravel cover present. Associated vegetation included species of Leucadendron and members of the families Cyperaceae, Iridaceae, and Restionaceae. The habitat of D. regia depends on periodic fire sweeping through and keeping the larger plants from choking out D. regia. Frost occurs infrequently in the valley.
Conservation status In a 2009 report of a 2006 trip, botanist Andreas Fleischmann noted that the higher elevation site is overgrown with plants of the family Restionaceae and he could not locate any remaining D. regia. The lower elevation site was in a similar state, but he recorded approximately 50 mature plants, making this one of the most critically endangered Drosera species.Fleischmann, A. 30 April 2009. Wild Drosera regia. CPUK Forum. Retrieved 21 December 2009. While D. regia has not been evaluated under the current International Union for the Conservation of Nature and Natural Resources (IUCN) standards for a rating on the Red List of Threatened Species, the International Carnivorous Plant Society recognised D. regia on their list of imperiled carnivorous plant species.Rice, B. A. 2003. Appendix: Imperiled Carnivorous Plant Species List. International Carnivorous Plant Society. Retrieved 21 December 2009. Drosera regia was also listed as "rare" on an early IUCN report in 1997,Walter, K. S., and Gillett, H. J. [eds]. 1998. 1997 IUCN Red List of Threatened Plants. International Union for the Conservation of Nature and Natural Resources. p. 240. but these earlier IUCN assessments were often poorly documented and are thus not relied upon today.International Union for Conservation of Nature and Natural Resources. 2010. Red List Overview. The IUCN Red List of Threatened Species. Retrieved 9 January 2010. Several other authors have identified how rare D. regia is in the wild, even calling it "threatened with extinction".Barthlott, W., Porembski, S., Seine, R., and Theisen, I. 2007. The Curious World of Carnivorous Plants: A Comprehensive Guide to Their Biology and Cultivation. Portland, Oregon, USA: Timber Press. pp. 94–106.
The short-term prognosis for natural populations of D. regia was greatly improved when a fire swept through its habitat in 2015. A team from Stellenbosch Botanical Gardens found new populations in the lower elevation zone and rediscovered plants in the higher elevation zone.
Taxonomy and botanical history Drosera regia was originally described by South African botanist Edith Layard Stephens in 1926.Schlauer, J. 2009. World Carnivorous Plant List – Nomenclatural Synopsis of Carnivorous Phanerogamous Plants. . Retrieved 26 December 2009. The binomial name Drosera regia is derived from the Greek word droseros, meaning "dew-covered" and the specific epithet regia comes from the Latin for "royal", a reference to what Stephens described as its "striking appearance". The genus is collectively referred to as the sundews, while Drosera regia is commonly referred to as the king sundew. Stephens was informed about this new species by Mr. J. Rennie, who had found several plants growing by a stream in the upper end of "Baviaans Kloof" on Easter in 1923. Additional specimens were located directly above this site on a plateau between South Ridge Peak and Observation Point. A second population was located in 1926 about away below the Slanghoek Peak near the headwaters of the Witte River.