| Drosera anglica | |
|---|---|
 | |
Scientific classification | |
| Kingdom: | Plantae |
| Clade: | Tracheophytes |
| Clade: | Angiosperms |
| Clade: | Eudicots |
| Order: | Caryophyllales |
| Family: | Droseraceae |
| Genus: | Drosera |
| Subgenus: | Droserasubg. Drosera |
| Section: | Droserasect. Drosera |
| Species: | D. anglica |
| Binomial name | |
| Drosera anglica | |
| Synonyms[2] | |
List
| |
Drosera anglica, commonly known as theEnglish sundew[3] orgreat sundew,[4] is acarnivorousflowering plant species belonging to thesundew familyDroseraceae. It is atemperate species with acircumboreal range,[2] although it does occur as far south asJapan, southernEurope, and the island ofKauai inHawaii, where it grows as atropical sundew. It is thought to originate from anamphidiploid hybrid ofD. rotundifolia andD. linearis, meaning that a sterile hybrid between these two species doubled its chromosomes to produce fertile progeny which stabilized into the currentD. anglica.[5]
Drosera anglica is aperennial herb which forms an upright, stemlessrosette of generallylinear-spatulate leaves. As is typical forsundews, the laminae are densely covered with stalked reddish coloredmucilaginous glands, each tipped with a clear droplet of a viscous fluid used for trapping insects. The lamina, which is 15–35 millimetres (0.59–1.38 in) long,[6] is held semi-erect by a long petiole, bringing the total leaf size to 30–95 millimetres (1.2–3.7 in). Plants are green, coloring red in bright light. In all populations except those inKauaʻi,D. anglica forms winter resting buds calledhibernacula. These consist of a knot of tightly curled leaves at ground level, which unfurl in spring at the end of thedormancy period. The root system is weak and penetrates only a few centimeters, serving mainly as an anchor and for water absorption. Nitrogen is in short supply in bogs and trapping and digesting insects provides an alternate source.
Drosera anglica flowers in the summer, sending uppeduncles 6–18 centimetres (2.4–7.1 in). long bearing several white flowers which open individually. Like other sundews, the flowers have five sepals, petals, and stamens with threestyles. The petals for this species are 8–12 mm (¼ to ½") long, and the flowers have branched 2-lobed styles.[6] The odorless, nectar-less flowers do not rely on insect pollinators for pollination, rather setting seed well through self-pollination (autogamy).[7] The black roundish spindle-shaped seeds,[8] are 1 to1+1⁄2 mm long. The fruits are a dehiscent three-valved capsule.
Like all sundews,D. anglica uses stalkedmucilaginousglands called tentacles which cover its laminae to attract, trap, anddigest smallarthropods, usually insects.[9] These are attracted by a sugary scent exuded by the glands, and upon alighting on the plant adhere to the sticky drops of mucilage. Although most of its prey consists of small insects such as flies, bulkier insects with large wings are also caught. Small butterflies,damselflies, and even dragonflies can become immobilized by the plant's sticky mucilage.
The plant's initial response to contact with prey consists ofthigmotropic (movement in response to touch) tentacle movement, with tentacles bending toward the prey and the center of the leaf to maximize contact.D. anglica is also capable of further movement, being able to bend the actual leaf blade around prey to further thedigestion process.[9] Tentacle movement can occur in a matter of minutes, whereas the leaf takes hours or days to bend. When something gets caught, the tentacles touching the prey exude additional mucilage to mire down the prey, which eventually dies of exhaustion or is asphyxiated as the mucilage clogs itstracheae. Once the prey has been digested and the resulting nutrient solution has been absorbed by the plant, the leaf unfurls, leaving only the prey'sexoskeleton behind.
Drosera anglica was given its first scientific description and named by the botanistWilliam Hudson in 1778.Constantine Samuel Rafinesque proposed moving it and other species to a new genus namedAdenopa in 1837, but this was not accepted.[2]
Drosera anglica grows in open, non-forested habitat with wet, often calcium-rich soils. These includebogs,marlfens,quaking bogs, cobble shores, and othercalcareous habitats.[10] This tolerance ofcalcium is relatively rare in the rest of the genus.D. anglica is often associated with varioussphagnum mosses, and many times grows in a soil substrate that is entirely composed of living, dead, or decomposed sphagnum. The sphagnum wicks moisture to the surface while simultaneously acidifying it. What soil nutrients are not seeped away by the constant moisture are often used up by the sphagnum or made unavailable by the lowsoil pH. Since nutrient availability is low, competition from other plants is diminished, allowing the carnivorous English sundew to flourish.
Drosera anglica is one of the most widely distributedsundews in the world. It is generally circumboreal, meaning that it is found at high latitudes around the globe. In a few areas, however, it is found farther south, particularly in Japan, southern Europe, the Hawaiian island ofKauaʻi, and California. Plants from Hawaiʻi, where it is known asmikinalo, are generally smaller than normal and do not experience a winter dormancy period. Its natural habitat includes 12 U.S. states, includingAlaska, and 11 Canadian provinces and territories.[1] The altitudinal range is from 5 metres (16 ft) to at least 2,000 metres (6,600 ft).[10][11]In the US state ofMinnesota, it was found in 1978 growing in shallow pools in peatlands withminerotrophic water dominated by low growing mosses andsedge species; because of its limited to small populations, and the type of microhabitats that it occupies, it is listed as a threatened species in the state.[8]
All North AmericanDrosera species except forD. anglica have achromosome count of 2n=20. In 1955, Wood noted thatD. anglica had a chromosome count of 2n=40, and hypothesized that it was ofhybridamphidiploid origin.[12] Since the leaf morphology ofD. anglica is an intermediary between that ofD. rotundifolia andD. linearis and the two occursympatrically in several locations, Wood conjectured thatD. anglica likely originated from a hybrid between these two.[12]
All North AmericanDrosera species produce sterile hybrids. The natural hybridD. rotundifolia ×D. linearis (conventionally but incorrectly referred to asDrosera ×anglica), is also sterile but ismorphologically similar to the modernD. anglica.[5] Errors in meiosis during ovule and pollen production, however, can result in a chromosome doubling which can allow forviable seed to be produced. The resulting plants, known as amphiploids, would be fertile. Woods noted that this appeared to be an ongoing process withD. anglica speciating fromD. rotundifolia ×D. linearis through amphidiploidy in multiple locations.[12] The question remains as to whyD. anglica is so widespread, whereas the range ofD. linearis is limited to theGreat Lakes region of North America. The greater adaptability ofD. anglica to varied habitat conditions could be a major factor.[5]
Drosera anglica was first described byWilliam Hudson in 1778. It has frequently been confused with the other circumpolar long-leafDrosera,D. intermedia. This confusion was fueled by the resurfacing of an older name,D. longifolia (described byCarl Linnaeus in 1753), which was regarded as being too ambiguous in description and had been applied to specimens of bothD. anglica andD. intermedia. Herbarium specimens were also a mix of the two species. These points ledMartin Cheek to proposeD. longifolia for rejection as a species name in 1998.[13] The proposal was accepted and the taxon listed as rejected in 1999.[14]
Several naturally occurringhybrids involvingD. anglica exist. These include:
| D. anglica ×capillaris | =D. × anpil |
| D. anglica ×filiformis | =D. × anfil |
| D. anglica ×linearis | |
| D. anglica ×intermedia | =D. × anterm |
| D. anglica ×spatulata | =D. × nagamoto |
| D.linearis × anglica | =D. × linglica |
| D.rotundifolia × anglica | =D. × obovata |
These are all sterile. In addition, severalman-made hybrids have been made.
