Carnivorous and Parasitic Plants: Adapt to Survive
Plants are often thought of as docile, passive creatures that are helplessly reliant on the soil in which they grow. However, some species of plants have shown, when their backs are against the wall, they can evolve some quite fascinating capabilities. Speaking realistically, nature at its core is not kind. Plants and all other forms of life must adapt in order to survive and multiply. In the plant kingdom, the will and need to survive has triggered some rather unique adaptations, resulting in several different species of plants that beckon us to rethink everything we think we know about plant growth and survival. These amazing plant groups have managed to break the so-called rules in order to benefit their own survival. Two enticing examples of which are those that have become carnivorous or parasitic.
There are over 600 documented species of carnivorous plants worldwide, spanning several different plant families. Carnivorous plants are most often flowering vascular plants (angiosperms) that have the ability to perform photosynthesis and receive mineral nutrients via their roots. Through the years, this type of plant has evolved the ability to capture and consume insects of various types and sizes. Though carnivorous plants have developed multiple styles of “traps,” the circumstances that have led to this type of adaptation are similar in nearly every instance.
In nature, carnivorous plants are found growing in areas such as bogs and marshes that lack the proper amounts of mineral nutrients (mainly nitrogen and phosphorus that encourage healthy plant growth and reproduction). The adaptation that led to the development of insect “traps” is one triggered by the lack of available nutrition. The leaves of carnivorous plants are where the adaptations have taken place, which have resulted in a variety of different style “traps.” They include pitfall traps (pitcher plants), flypaper style traps (sundews), snap traps (Venus flytrap), suction traps (bladderworts) and lobster-pot traps. Two popular carnivorous plants that can be grown at home, indoors and out, are Venus flytraps and pitcher plants.
Pitcher plants are generally placed into two main families, the old world family Nepenthaceae and the new world family Sarraceniaceae. The old world species grow mainly in trees and develop a rather primitive looking pitcher where as the new world species grow from rhizomes in the ground and form a more complex pitcher from an entire leaf. Pitcher plants have been found growing all over the world in bogs and marshes with substandard sources of nitrogen (N).
Two popular species in North America are the Sarracenia and the Darlingtonia (native to northern California and Oregon). Both are members of the new world family of pitcher plants. Their pitchers create nectar that attracts insects and, once said insect is lured into the pitcher, the nectar traps them. An enzyme, much like our own digestive enzymes, slowly kills and breaks down the constituent proteins within the insect.
After the proteins are completely broken down, the plant is able to utilize the nitrogen (N) contained within. Pitcher plants can be grown at home, both inside (under T5 florescent lights) and out. The important thing to remember is to simulate their natural environment as closely as possible. This requires using a growing medium that is inert and completely free of any mineral nutrient charge. Remember, use absolutely NO fertilizer. Pitcher plants have evolved to become carnivorous because of an extreme lack of mineral nutrition and that is what they thrive on.
Venus flytraps (Dionaea muscipula) are native to the nutrient deficient swamplands and bogs of North and South Carolina. They are carnivorous plants that prey on insects with the help of some very uniquely shaped leaves. The leaf blade is comprised of two lobes hinged together at a midrib. The surface of the leaf has what are referred to as trigger hairs.
When two or three of the trigger hairs are touched consecutively in a small amount of time, the trap snaps shut, trapping the insect inside. The trap is lined with teeth-like cilia that interlock with each other when the trap is closed. This makes escape for the insect nearly impossible. With the insect trapped inside, the leaf begins to create the digestive enzymes that will break the now dead insect down into proteins and then into an available nitrogen source.
Venus flytraps can also be grown at home, inside (under T5 fluorescent lighting) or out. Once again use a potting soil that is void of mineral nutrients and do not fertilize. Venus flytraps, as well as pitcher plants, can be watered rather frequently and grow well when consistently wet.
Most types of carnivorous plants are native to areas that are threatened by human development. Much effort has been made to protect these lands, but the threat is still there. This is why it is important to buy carnivorous plants for growing at home from reputable growers that start the plants by either splitting the rhizomes or from tissue culture propagation. In almost all cases, it is illegal to gather carnivorous plants from the wild and those who get caught doing so are levied with heavy fines.
Parasitic plants offer up yet another amazing sector of plant life. This group of vascular plants has adapted the ability to fend for themselves in conditions that lack available nutrients or where the competition for nutrients is extreme. Parasitic plants vary from those which are fully photosynthetic to those which are just barely. As the name implies, parasitic plants have circumvented the need to find nutrients in a small plot of soil by the development of a modified meristem root called a haustorium. A haustorium can penetrate the vascular system of another plant, called a host, stealing vital mineral nutrients, water and carbohydrates for its own benefit. This type of interaction can often result in fatality for the host plant. Parasitic plants can attack a host in a variety of ways ranging from an attack of the roots to an attack of the vascular tissue found in the stems. Two examples of parasitic plants that are somewhat well known are the several different species of mistletoe and the dodder vine.
The dodder vine (Cuscuta) is a wispy plant with thin stems that attaches to a host plant’s stems via its haustorium (modified root). The haustorium will effectively reroute any water and mineral nutrients coming up from the roots, as well as any carbohydrates coming down from the leaves, directly to the roots of the dodder plant itself. Dodder seeds are very small and contain little initial sustenance, so it is paramount that the dodder seedlings find a suitable host to feed upon within a few days or they may surely die. Dodder has the ability to aggressively attack a host, quickly engulfing it and eventually killing it. This is why dodder is deemed a definite threat to agriculture, especially in 3rd world and developing countries, and requires a considerable amount of thought and attention on how to go about eradicating the plant from fields and pasture land.
The plant family Loranthaceae is host to multiple species of mistletoe. The most common of which is the species Phordendron serotinum, the eastern mistletoe. This is the type that has been a staple of the holiday seasons for years.
Eastern mistletoe is a flowering vascular plant that grows on the branches of trees where mineral nutrients are not present. Mistletoe is able to perform photosynthesis, but it receives a majority of its mineral nutrient needs (via its haustorium) from the vascular system within the host trees branches.
This adaptation is likely due to the fact that after birds eat the mistletoe berries, they often excrete the remaining seeds onto the branches of the trees they frequent. The mistletoe seeds have in turn developed a sticky exterior which allows them to stick to the tree branches where they will germinate and grow. Growing on the branches of a tree helps keep the mistletoe plants safe from possible predators, but this is also an environment that is nearly void of any mineral nutrition. Mistletoe plants, in order to prolong the life of a species, parasitize the host tree and obtain needed nutrients to the detriment of the host itself.
Carnivorous and parasitic plants are two great examples of the fact that in nature, where the inability to adapt will almost certainly lead to the death of a species, plants are not as passive as they may seem. Several species throughout many different plant families have taken survival into their own hands with the development of certain appendages that have truly changed the game in terms of normal plant behavior. These fascinating types of plants serve as unique reminders that nature, without compromise, is unendingly complex and constantly changing.