Predator and Prey

Drosera rotundifolia

December 9, 2011, 8:57 am
Content Cover Image

Drosera rotundifolia, Czech Republic, Šumava. Source: Ondřej Zicha/EOL

Drosera rotundifolia is an insectivorous plant that occurs in marshes, bogs and fens in a circumboreal distribution; common names for this species are Roundleaf Sundew or Common Sundew. This species is designated of Least Concern by the IUCN; however, such a categorization is misleading, since Roundleaf Sundew is classified as an endangered species in certain of the United States as well as threatened in other world areas where it previously flourished. This taxon is also noted for its considerable medicinal qualities.

The detailed mechanisms of this carnivorous plant were first described in the nineteenth century, depicting the intricate nature of the tenacle attack on unwary insects. Subsequent entanglement of the prey and secretion of acidic digestive juices complete the cycle of predatory action.

Occurrence

caption Lithuanian bog habitat of D. rotundifolia on Scot's pine forest floor. @ C.Michael Hogan D. rotundifolia is one of the most broadly distributed species within its genus. Not only is it found throughout much of Siberia, northern Europe and northern North America, but it also occurs in parts of Japan, and even as far south as Korea and New Guinea, where soil and moisture conditions are favorable. The distribution in Asia is not just circumboreal within Siberia and the Kamchatka Peninsula,  but also includes such regions as the Caucasus and Turkey, as well as Japan, and also the more unexpected southerly occurrences in South Korea and the island of New Guinea.

Within western Europe the species has been particularly well studied in England and Scotland with notable occurrences in the Pennines of Scotland and within England's Lake District, Shropshire as well as Exmoor, Dartmoor and Sedgemoor. Its European range also includes much of France, Germany, the Benelux as well northern Portugal and Spain. For Scandinavia and Europe's northwest islands, the Roundleaf Sundew is found in Sweden, Finland and Denmark as well as southern Norway and Iceland.The plant is also found in the Baltics in the Sarmatic mixed forests, central and eastern Europe. In Lithuania and Romania, for example; the range is not continuous over broad areas, but is specialised to boggy Scots Pine forested locales. Switzerland, Poland, Belarus and the Czech Republic also present established occurrences.

Within North America all regions of Canada manifest robust opportunities for the species, apart from tundra and prairies. Within the USA the distribution is chiefly favored in southern Alaska, the Applachian Mountains and the extreme northeast and northwest states; however, some populations are found as far south as Georgia and Louisianna.

Species description

The height of an individual plant is quite variable, and may reach 25 centimeters, although it is usually considerably less in stature. The characteristic diameter of the fully grown plant is on the order of two to five centimeters. Leaf structures manifest in a basal rosette, from the center of which emerges a thin lone glabrous stalk bearing white or pink flowers; moreover, the flowers are borne asymmetrically along one side of the slender stalk. Each flower displays five petals. The light brown coloured seeds of this species are 1.0 to 1.6 millimeters in length, with a tapered narrow shape. The plant's leaves are attached to narrow, hairy 1.5 to 5.0 centimeter long petioles. 

Carnivory mechanism

caption D. rotundifolia leaf with tenacles and glands. G.L.Goodale As Goodale was one of the first to point out, a striking feature of D. rotundifolia is the thick assemblage of glandular hairs on the leaves; from the tip of each hair exudes a drop of clear viscid liquid. The marginal tenacles exhibit an elongated stature, and are terminated by purplish glands. The hairs at the leaf middle are more abbreviated in length and manifest green stalks with ovoid glands. Each of the glands contains a dual layer of polygon shaped shells that surround a central body.

When an animal prey alights on the inner glands of a D. rotundifolia leaf, the marginal tenacles begin to enter a torpid motion. Then suddenly these outer tenacles curve abruptly allowing the glandular tips to contact the prey. In some cases the leaf itself participates in the carnivorous enclosure of the prey.

Francis Darwin was the first to note that an object of mass as little as .0008 milligrams can initiate movement of the glandular hairs into capture mode. Once the tenacle has reached a state of excitement via contact, the cells in the vicinity of the glands evince a noteworthy transformation: instead of being full of uniform purplish fluid, the liquid content presents as purplish flecks in suspension within a transparent colorless fluid. Darwin was the first to note that these flecks exhibit very diverse geometries, from spherical, to oval to highly elliptical, and often most irregular, with club like projections.

Darwin was also the first to note that the glandular and tenacle excitation greatly increases if the prey has extractable nitrogenous chemicals. In this case not only is the tenacle action more robust, but an acidic secretion is initiated that accelerates the disintegration and subsequent digestion of the prey. When an insect tries to escape, that motion only serves to excite the tenacle and glandular activity, thus accelerating the predation efficacy.

References

  • George Lincoln Goodale. 1885. Physiological botany (Google eBook) Ivison, Blakeman. 535 pages
  • C.Michael Hogan, Curator. Encyclopedia of Life. Drosera rotundifolia L.
  • Karen Legasy, Shayna LaBelle-Beadman and Brenda Chambers. 1995. Forest Plants of Northeastern Ontario. Lone Pine Publishing, Ontario.
  • D.H.Paper, E.Karall, M.Kremser and L.Krenn. 2005. Comparison of the antiinflammatory effects of Drosera rotundifolia and Drosera madagascariensis in the HET-CAM assay. Phytotherapy Research 19 (4): 323–6
Glossary

Citation

Hogan, C. (2011). Drosera rotundifolia. Retrieved from http://www.eoearth.org/view/article/51cbed6a7896bb431f6921a7

0 Comments

To add a comment, please Log In.