Drosera rotundifolia : Round-Leafed Sundew

 

 

 

 

 

Identifying Characteristics:

 

Drosera rotundifolia is an easily identifiable carnivorous perennial. Found mostly in wetland habitats, D. rotundifolia is characterized by its tentacle-like stalks and round leaves that grow in a basal rosette pattern. The leaves are covered with bright red, hair-like structures that are tipped with "dew-like" glands that persist throughout the entire day. The root system is shallow and fibrous, providing mostly anchorage. 2-6 inch flower structures grow as one-sided racemes that can occur with 2-15 flowers. These tiny flowers are white and open exclusively during the daytime (Matthews 1994).

 

 

 

Distribution:

 

State Distributional Map for DRRO

                                                              Image courtesy of the USDA

 

 

The family Droseraceae is quite possibly the most diverse carnivorous plant family, including 150-160 species found worldwide: Europe, Asia, Africa, North and South America. Native to North America, D. rotundifolia is one of eleven Sundew species in the U.S. (Rice 2002). It can be found in sphagnum-dominated wetlands on both the east and west coast, in addition to the Midwest. The distribution ranges from southern California to Alaska, and from Florida to Nova Scotia (Matthews 1994). It is fairly common within the Great Lake’s region. Europe and Asia are also home to the species D. rotundifolia.

 

Natural History:

 

Habitat Requirements:

Found mostly in sphagnum-dominated wetlands, D. rotundifolia inhabits low-nutrient environments due to its ability to capture and digest a variety of insects. Bogs embody the ideal conditions for these plants, due to the high substrate saturation, high acidity, low nutrients and high amounts of peat, or dissolved organic material.

The moisture requirements of D. rotundifolia restrict its habitat choices to only those with a high water table, roughly from 1 inch above to 16 inches below the soil surface (Matthews 1994). Sphagnum moss has impressive moisture retention abilities, which therefore makes it an ideal substrate to keep D. rotundifolia hydrated.

            Living in an oligitrophic, acidic environment allows D. rotundifolia to reach the fullest of it’s competitive potential. The nutrient requirements of most non-carnivorous vascular plants cannot be fulfilled in bogs because of the acidic pH and lack of “soil.” Carnivorous plants have developed a special adaptation that allows them to obtain nutrients from the surrounding environment as opposed to the soil. They are therefore able to grow most readily in wetland habitats, whereas in other environments, they would most likely be out-competed by non-carnivorous plants (Rice 2002).

Being a relatively short plant, D. rotundifolia cannot thrive in a shaded environment. If higher plants begin to take over, it may affect the development of the Sundew. A spindly habit may develop as opposed to the typical rosette.

                          

Nutrition:

            Nutrients such as nitrogen, phosphorus, calcium, magnesium, and potassium are essential to for the growth and productivity of all plant-life. Non-carnivorous plants are able to take up these valuable nutrients from the surrounding soil, through their roots. Due to the fact that D. rotundifolia grows in highly saturated environments lacking true “soil”, it is necessary for them to obtain nutrients in an alternative manner. Like many of it’s carnivorous collogues, D. rotundifolia has developed adaptations that allow it to capture and digest various types of insects in order to survive in oligitrophic environments (Rice 2002).

            The tips of the stalks are adorned with glands that contain nectar, digestive enzymes and adhesive compounds. Insects are attracted to the enticing nectar, but upon landing on one of these “dewdrops,” they are instantly trapped in a sticky mess. In many cases, the actual landing of the insect can stimulate surrounding stalks, which causes them to collapse and enclose the prey. It is even possible that the entire leaf may enclose upon the insect. Rendered completely immobile, the insects are soon digested with the help of several digestive enzymes (Rice 2002).

            An interesting consideration is the observation that nutrition can in fact affect and determine plant morphology. “Differences in leaf morphology and orientation are reflected in numbers and types of arthropods captured (Krafft & Handel).”

 

                

 

 

 

 

Reproduction:

            A necessary element of life, reproduction in plants can occur either sexually or asexually. D. rotundifolia possesses the capabilities of reproducing either by seed or through vegetative (asexual) growth.

            Sexual reproduction: D. rotundifolia is an angiosperm, therefore possessing flowers and undergoing the typical life cycle of a flowering plant. The process of pollination can occur via insects or wind, or if all else fails, through self-pollination. Once pollination occurs, seeds will eventually form within the ovary, producing a fruit. In order to be released for dispersal, the seeds must wait until the fruit begins to rot. Then begins the process of seed dispersal, and they are carried near and far, typically through animals, wind or water (Matthews 1994).

            Asexual reproduction: D. rotundifolia are able to produce a supplementary rosette from an auxiliary bud. At first it is attached to a pre-existing tentacle, but that tentacle soon dies, and the new rosette is able to completely separate and become self-sufficient. Another form of vegetative reproduction occurs when new plantlets are formed at the axils of lower leaves (Krafft & Handel).

                           

                                                                                    Jim Stasz @ USDA-NRCS PLANTS Database

 

 

 

 

Interactions:

The primary interactions that concern D. rotundifolia are those in relation to arthropods. Being an insectivorous plant, D. rotundifolia obtains its nutrients from the digestion of trapped insects. Its survival is therefore dependent upon a healthy insect population. Not only are the insects critical for nutrition, but also, they are critical for crosspollination (Rice 2002).

 

           

 

Human Interest:

 

The title “carnivorous plant” almost seems like an oxymoron to many of us. We have been taught that plants are autotrophic, in that they are able to harness their own energy. To view a plant as being a predator contradicts all that we have been taught. Perhaps it is this mere thought that evokes such interest in these carnivorous plants. Furthermore, it could be argued that this interest has led to the discovery of many uses and applications:

 

  Medicinal Uses-

        Used as an antibiotic to combat bacteria infections: Streptococcus, Staphylococcus, and Pneumococcus. It is also effective in respiratory relief of afflictions such as bronchitis, whooping cough, and asthma. There has been some discussion as to its effectiveness in treatment of warts and corns (Matthews 1994)

 

Cultural Usage-

Due to its ability to curdle milk, Drosera leaves are sometimes used by the Swedish to make cheese.

 

  Superstitions-

            During the middle ages, French sorcerers believed that, when rubbed upon the skin, the “dew” of Drosera plants would transform them into inexorable beings. Collections were made at midnight on St. John’s Eve; however, the collectors had to be careful they were not being followed by the devil. In order to accomplish this, they had to walk backwards (Rice 2002).

 

Ecology/Conservation Issues:

 

Due to the specific habitat requirements of most carnivorous plants, we are able to use them as indicator species of various environmental conditions. As previously stated, D. rotundifolia will only thrive in an oligitrophic, saturated environment with a high water table. We can therefore use it as an indicator of these conditions, and use this species to monitor the evolution of a specific ecosystem. In addition to general habitat requirements, D. rotundifolia needs high water quality and low anthropogenic pollution. These requirements could also be used to indicate situations in which water quality is being reduced, or pollution is increasing due to land development (Rice 2002).

Following trends of wetland habitat destruction, D. rotundifolia is rapidly becoming seriously endangered. It is estimated that within the United States, roughly “3-5% of carnivorous habitats remain (Rice 2002).” According to the USDA, the following table provides the status of  D. rotundifolia within each listed state:

 

 

                                                    Threatened and Endangered Plant Information:


This plant is protected by the U. S. federal government or a state. Common names are from state and federal lists. Click on a place name to get a complete protected plant list for that location.

Illinois:

       round-leaved sundew

    Endangered

Iowa:

       roundleaved sundew

    Endangered

New York:

       sundew

    Exploitably Vulnerable

Tennessee:

       roundleaf sundew

    Threatened