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:
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: |
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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. |
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References: |
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