Flypaper Sticky Hairs

Aeonium, Erica, Geranium, Hydrolea, Linnoea, Lycopersicon, Mirabilis, Nicotiana, Pelargonium, Platylepis, Primula, Proboscidea, Saxifraga, Solanum, and Sparmannia.

PLANTS DISPLAYING ACTIVE TRAPPING CHARACTERISTICS

These are plants in which rapid movement of the plant is involved in capturing prey.

Caltha dioneaefolia, which grows in Tierra del Fuego in Argentina, was first described by Dr. Hooke in 1874. He wrote "Delpino, for example, has suggested that a plant, first described by myself from Tierra del Fuego—Caltha dioneaefolia—is so analogous in the structure of its leaves to Dionaea that it is difficult to resist the conviction that its structure is also adapted for the capture of small insects." Another plant, Molinia coerulea, is a grass whose flowers have bracts which act as the jaws of a spring-type trap and can capture insects for a period of time during flowering.

DEVELOPMENT OF CARNIVORY

Plants and animals have evolved to fill all available habitats and ecological niches. Plants inhabit every possible environment including water, air, soil (wet and/or dry), other plants and also animals.

Green plants contain the organic pigment chlorophyll. When provided with light, carbon dioxide, water, and essential minerals they produce carbohydrates through a chemical process called photosynthesis mediated by the pigment chlorophyll. The light energy is converted into the chemical bond energy of a food molecule. The carbohydrate food molecules are utilized by the plant for cellular energy and as the basis for producing other molecules which are essential for the plant's growth and development. Usually the minerals and water are taken up by the root system and conveyed throughout the plant, including the sites of photosynthetic activity.

Plants have evolved to utilize all available habitats such as arid and semi-arid regions, moist and waterlogged areas, full sunlight to complete shade, from tropical to Arctic climates. Thus, it would be logical to expect that plants would evolve to survive in nutrient-poor soils and/or water.

The evolution of carnivorous plants is speculative due to the paucity of the fossil record. Flowering plants (angiosperms) began to evolve during the Cretaceous period of the Mesozoic Era. The flowering carnivorous plants, the topic of this book, therefore, cannot be older than 136 million years. The oldest carnivorous plant fossil is Aldrovanda pollen found in rock of the Eocene period that began 53 million years ago and ended 37 million years ago. The earliest Droseraceae pollen is found in the Miocene period, 26 to 12 million years ago.

Many plants today are adapted to foliar feeding. That is, when a nutrient (fertilizer) solution is sprayed on the leaves, the plant can absorb the nutrients through the leaves into the plant body. The beginning of carnivory could have taken place when some leaves formed shallow depressions in which rain water was retained for a period of time after a rain shower. These leaves would be ideal water reservoirs for insects. In the process of obtaining a drink, some insects would drown and eventually be decomposed by bacteria living in the water. The nutrients released into the water could have been absorbed by the leaf into the plant body. This process, similar to foliar feeding, would provide a distinct advantage to plants growing in nutrient-poor soils barely able to provide sufficient nutrients for growth. It would have provided them with a distinct survival advantage. The deeper the depression in the leaf, the more insects could be drowned and decomposed. In times of stress or overcrowding the plants that could derive nutrients through their leaves would be better able to compete in nutrient-poor soil. The plants able to obtain additional nutrients from their leaves would be stronger and healthier and more likely to produce offspring. As time passed, those plants that evolved more effective traps, means of attracting insects and directional guides—that is, the arrangement of nectar-producing glands and hairs that lead the prey into the trap— would be better able to survive in nutrient-poor soils.

The characteristics that distinguish carnivorous plants—such as visual and odiferous lures, directional guides, secreting glands, absorbing glands, trapping, and rapid movement—are found in various plants not considered carnivorous. Some non-carnivorous plants trap insects to effect pollination. Plants such as Mimosa pudica and the Telegraph plants (Desmodium) have leaves that exhibit rapid motion. Some tree leaves secrete a sticky substance that falls to the ground. While all of the individual characteristics of carnivorous plants can be found in other plants, when they are all combined in the same plant the organism is truly unique, a carnivorous plant whose modified leaves can trap and digest prey lured to the plant. The digested materials are utilized by the plant for its growth and development. The fascination with carnivorous plants partly stems from the ability of these plants to reverse the order we expect to find in nature. Carnivorous plants are the predators rather than the passive prey.

PLANT NAMES

Common names used for plants usually are descriptive but confusing because the same plant may be called by different names in different geographic areas. One common name used for carnivorous plants, Fly Catcher, can refer, for example, to a member of the genus Sarracenia or the genus Dionaea. Another disadvantage of using common names is that they are not easily recognizable by people speaking other languages. In addition, plants from widely separated genera may have the same common name; common names may suggest relationships that do not exist; and there is no international body for governing common names. To remedy these problems a Latinized binomial system was adopted about a century ago. For the reasons noted in this paragraph binomial names are used in this book.

The binomial system had its beginnings in the sixteenth century and was used by the botanists Brunfels and Dodonaeus. Carolus Linnaeus, in the eighteenth century, standardized and popularized the binomial system, which was adopted in 1867 by the First Botanical International Congress in Paris. The system (International Code of Botanic Nomenclature) is under constant review, and changes are made when necessary. Even though the system is not perfect, it does provide only one name for each species of plant. No two plants can have the same genus and species name.

In the binomial system plant names are Latinized because at the time of its development, Latin was the universal language of scholars. The name consists of two words: the first word, the genus name, is capitalized; and the second word, the species name, is not. These terms often describe some characteristic of the plant. For example, Drosera, a genus name, is derived from a Greek word meaning dew and refers to the droplet of mucilage on the ends of the tentacles. In the binomial name, Drosera rotundifolia, the species name rotundifolia refers to the plant's round leaves. Genus and species names are italicized when in print and when written or typed, the binomial is underlined. In technical writing the binomial name is followed by the name or standard abbreviation of the person's name who officially described the plant. If there has been controversy over the plant and its name has been changed, there may be more than one person's name following the binomial name—for example, Sarracenia purpurea f. heterophylla (Eaton) Fernald. The names of individuals are not italicized.

A genus consists of a group of plants which have very similar characteristics. For example, the genus Felis includes all cats, which have many common features. In the cat population there are cats that are sufficiently different from the other cats to be subdivided into a smaller group; this is done with a species name. Thus, the household cat is Felis catus, while the tiger, another member of the cat family, is Felis tigris and the cougar is Felis concolor.

There are finer subdivisions than species. These are in order of decreasing distinction, along with their abbreviations in parentheses, as follows: subspecies (ssp.), form (f.), and variety (var. or v.).

The members of a species have many similar characteristics, but in some cases there are enough minor differences to divide the members into two or more groups called subspecies. An example is Sarracenia purpurea ssp. purpurea and Sarracenia purpurea ssp. venosa.

Within the population of Sarracenia purpurea ssp. purpurea there are members distinguished from the rest by the absence of red coloration. This group is a division of a subspecies and called a form. The correct name for the plants lacking red coloration is Sarracenia purpurea ssp. purpurea f. heterophylla. If there are some differences in the members of a form, they are designated as a variety.

Subdivisional names are italicized but the reference names or abbreviations are not. Either reference names or their abbreviations can be used. This is illustrated by the following examples, Sarracenia purpurea subspecies purpurea form heterophylla, or Sarracenia purpurea ssp. purpurea f. heterophylla.

Once the full name of a plant is used in a discussion and as long as the genus discussed is not changed, the genus name can be abbreviated in further references. For example, after the binomial Drosera binata is used once, its further use in the same document is written D. binata.

Even though one genus may be quite distinct from another there are groups of genera (plural of genus) which have enough similarities that they are grouped into families. This is illustrated in chart 1, where the 7 families and 15 genera of carnivorous plants are listed.

HYBRIDS

Hybrid plants are produced from two different species or hybrids. Hybrids may occur spontaneously in the wild as the result of natural agents carrying the pollen from the flower of one species to another. Or, hybrid crosses may be made by plant breeders.

Hybrids are identified by one or both of two names: the formula name, or the collective epithet. For example, the formula name of one Sarracenia hybrid is Sarracenia minor X Sarracenia psittacina. This formula indicates the parentage of the hybrid. In usual practice the female parent producing the seed is listed first in the formula name. If this information is unknown, then the parental species are listed alphabetically.

The collective epithet for all hybrid plants resulting from the cross between S. minor and S. psittacina is Sarracenia X formosa. The "X" before the second name indicates that the plant is a hybrid. When Sarracenia are under discussion, the formula name is often written S. minor X S. psittacina, and the collective epithet as S. X formosa.

The collective epithet may also be a word or a phrase of not more than three words in a modern language. The hybrid designation for the cross S. alata X S. psittacina, for example, is Sarracenia (Robin Louise). In this case the "X" is omitted and the collective epithet placed in parentheses following the genus name.

Cultivars

A hybrid which shows exemplary characteristics that distinguish it from the other hybrids of the same parentage may be designated as a cultivar. "Cultivar" is a term which indicates a plant created by man. The term was formed from the two words "cultivated" and "variety." It is used to denote a group of cultivated plants that are distinctive from other members of the same group (grex), whether it be a species, subspecies, variety, or a hybrid of plants in cultivation or in the wild. The difference between a cultivar and other members of the same group resides in such characteristics as color, shape of leaves, size, or floral configuration.

Cultivars may arise or be developed by hybridizing species or hybrids; selecting the best seedling of a self-pollinating cultivar; inbreeding; and propagating natural and/or induced mutations. A cultivar may be derived from cultivated plants or may be found in a natural population of plants. The cultivar must be propagated by seed if it is an annual; but if a perennial, vegetative means of propagation are used in order to maintain its distinguishing characteristics. Sometimes a characteristic that was distinctive in a plant is not heritable; that is, it does not show up in plants propagated from a selected plant. Such a plant cannot be considered a cultivar. In order for a plant to be the basis of a cultivar, its particular identifying traits must be named according to the rules codified in the International Code of Nomenclature for Cultivated Plants (latest edition, 1980). Such cultivars must have fancy names; that is, not a botanical name in Latin form. (But cultivar names published prior to 1959 may be botanical names in Latin form.) A cultivar from a hybrid is designated by adding a fancy name to the hybrid's collective epithet or the formula name. The fancy name is preceded by 'cv.' or is enclosed in single quotation marks. For example, if a plant from the cross S. alata X S. psittacina displayed inheritable vivid red blotches, it could be designated as the cultivar 'Red'. The proper name would be Sarracenia (Robin Louise) cv. Red, or (Sarracenia alata X S. psittacina) 'Red'.

Discretion should be exercised in the naming of new cultivars so that the distinctions are not based on minor or trivial differences.

To make new cultivar names legal or valid, the name and a description of the plant indicating its difference from other plants in the same group, along with the parentage and history and, if possible, a diagram or photograph, must be published and distributed to the public. Publication is accomplished by having it appear in a dated catalog, book, periodical, or by photocopy, ditto, or mimeograph, with distribution to a significant number of people.

The cultivar name should also be registered with the registration authority designated for the genus. The job of the registration authority is to catalog cultivar names and descriptions to prevent both duplication of names and the same cultivar being assigned more than one name. For example, suppose you develop a cultivar and decide to call it Sarracenia alata cv. Yellow Gem. You send the description of the plant, along with the name, to the registration authority. The registrar checks previous registrations to determine if the name has already been used by someone else, and also if the cultivar you "developed" has already been registered by someone else. If the former, you simply choose another fancy name and resubmit your application. If the latter, you have no choice but to drop your cultivar name and work on developing another cultivar.

Unfortunately, at this time there is no designated registration authority for carnivorous plants.

For additional information on cultivar naming and registration, consult the International Code of Nomenclature for Cultivated Plants—1980, which is in many libraries and available through the American Horticultural Society, Mt. Vernon, Virginia, 22121.

While the foregoing section may seem complicated and pedantic, it is the simplest and most accurate way to deal with plants.

CLASSIFICATION OF CARNIVOROUS PLANTS

Of the one-quarter of a million species of flowering plants about 600 are carnivorous. They are divided into two groups based on corolla structure, Choripetalae and Sympetalae. The group of plants categorized as carnivorous belong to 7 families and 15 genera. Family names can be recognized by their suffix, which is 'aceae.' This classification is illustrated in Chart 1.

Chart 1

Choripetalae Group

Byblidaceae

Byblis Cephalotaceae Cephalotus Dioncophyllaceae Triphyophyllum Droseraceae Aldrovanda Dionaea Drosera Drosophyllum Nepenthaceae

Nepenthes Sarraceniaceae Darlingtonia Heliamphora Sarracenia

The plants in the Sympetalae group have flowers which are personate. Personate flowers have petals that are joined or fused together forming a two-lipped corolla terminating in a tube. They exhibit bilateral symmetry, having only one plane that can be drawn through the flower that will divide it into two parts that are mirror images of each other.

The plants in the Chloripetalae group have flowers in which the petals are not joined together and the flowers exhibit radial symmetry, meaning the flower parts are arranged around a circle and can be divided into mirror images by any plane that passes through the center of the circle.

Sympetalae Group

Lentibulariaceae

Genlisea Pinguicula Polypompholyx Utricularia

Chart 2: List of genera, with their type of trapping mechanism and geographic range.

Number of

Genus

species

Geographic Distribution

Type of Trap

Aldrovanda

1

Europe, Asia, Africa, and Australia

Active

Byblis

2

Australia

Passive flypaper

Cephalotus

1

S.W. Australia

Passive pitfall

Darlingtonia

1

California & Oregon, U.S.A. Western Canada

Passive pitfall

Dionaea

1

North & South Carolina, U.S.A.

Active

Drosera

120

Omnipresent

Passive flypaper

Drosophyllum

1

Morocco, Portugal, and Spain

Passive flypaper

Genlisea

14

Tropical Africa & Tropical South America, Madagascar

Passive lobster

Number of

Genus

species

Geographic Distribution

Type of Trap

Heliamphora

6

Northern South America

Passive pitfall

Nepenthes

71

Area surrounding and including the East Indies

Passive pitfall

Pinguicula

50

Northern Hemisphere and South America

Passive flypaper

Polypompholyx

2

Australia

Active mousetrap, suction type

Sarracenia

9

North America

Passive pitfall

Triphyophyllum

1

West Africa

Passive flypaper

Utricularia

ca. 300

Omnipresent

Active mousetrap, suction type

TRAPPING MECHANISMS

The trapping mechanisms of carnivorous plants can be categorized as either active or passive with subdivisions in each group.

Active Trapping Mechanisms

An active trap is one in which rapid movement is an integral part of the trapping mechanism. There are two kinds of traps in this category, active "steel" trap and active "mousetrap" suction type.

Active steel type trap: Found in Dionaea and Aldrovanda. The trap consists of two lobes, which are rectangularly shaped, joined at the midrib and normally open. When stimulated the two lobes move rapidly toward each other and entrap the prey. The opening of the trap is a growth process and, therefore, much slower than the split-second closure.

Active mousetrap suction type: Found in Polypompholyx and Utricularia. The bladders or leaves which are roughly egg-shaped are the traps. At one end of the bladder is an opening with a door that opens into the trap. When the trap is set, the pressure inside the trap is lower than on the outside. The trigger hairs on the door set the trap off when touched by insects. Since the pressure inside the trap is less than the pressure outside the trap, the prey and water are sucked inside the trap. This is a purely mechanical trap, as distinguished from Dionaea and Aldrovanda traps which involve growth processes.

Passive Trapping Mechanisms

In passive trapping, rapid movement is not an integral part of the trapping mechanism. There are three types of passive traps: pitfall, lobster, and flypaper.

Pitfall: Found in Cephalotus, Darlingtonia, Heliamphora, Nepenthes, and Sarracenia. Trapping is accomplished when insects are lured by various methods to a cylindrically-shaped tube, which has been aptly called the stomach of the plant but is more often called the pitcher. The shape and embellishments of the pitchers vary considerably in the five genera and their species.

Lobster trap: Found in Genlisea. The prey is led into the trap by two spiral arms which have hairs that guide the prey. Once inside the trap the prey cannot get out.

Flypaper type (1): Found in Drosera. Prey is captured by becoming mired in the sticky mucilage produced by the tentacles that cover the upper surface of the leaves. The tentacles bend over to touch and force the prey down against the leaf surface. In many species prior to digestion the leaves will bend around and enclose the prey.

Flypaper type (2): Found in Pinguicula. Here as in the Drosera-type trap, the prey is entrapped by the sticky mucilage produced by the tentacles on the leaves, but in Pinguicula there is no movement of the tentacles. The margins of the leaves can roll up, forming a shallow basin.

Flypaper type (3): Found in Byblis, Triphyophyllum and Drosophyllum. The prey here is mired in the sticky mucilage as it is in Drosera and Pinguicula except there is no movement of either tentacles or leaves.

USE OF CARNIVOROUS PLANTS

Carnivorous plants have been used extensively for medication and other purposes. In the past, plants were virtually the only source of medicinal preparations. A plant such as Drosera that was able to retain its droplet of mucilage during the day without evaporation was believed to have extraordinary medicinal powers.

Drosera

Macerated Drosera leaves or extracts of leaves were used externally to treat warts, corns, and sunburn. Extracts or teas made from the leaves were used to treat internal disorders including tuberculosis, asthma, whooping cough, catarrh of the lower respiratory tract, arteriosclerosis, eye and ear inflammations, liver pain, morning sickness, dropsy, various stomach maladies, syphilis, toothaches, intestinal problems, as a tranquilizer, diuretic, and it was believed to have some aphrodisiacal power. When homeopathy was in vogue, the extract was also used to cause irritation of the skin because it was believed that if the skin was inflamed, an agent which caused inflammation would cure it. This is the theory behind producing and using vaccines for disease control. Scientists have discovered an anti-spasmodic agent in some Drosera species.

Pinguicula

The leaves were applied to cattle sores. Mixtures of extract of the leaves and linseed oil were used for treating wounds. Leaves or their extracts have been used to curdle milk and to make a milk-type dessert.

Nepenthes

The fluid in the unopened leaves was used to cure bed-wetters by pouring the fluid of the unopened pitchers on the head of the individuals, who later also drank some of it.

PRESERVING CARNIVOROUS PLANTS

Some species of carnivorous plants are in danger of extinction. Many people attribute this outcome to man's activity. This fundamentally is a false view. Evolution has been going on for eons. True, man has in some cases accelerated the process, but if man were not around, all bogs would eventually become dry land with trees growing in them. Natural geological processes will result in lakes becoming swamps and then dry land. Some of man's activities have certainly reduced populations of carnivorous plants, but the inevitable outcome of natural processes is another cause for diminishing plant numbers.

The prime human activity responsible for the reduction in numbers of some species of carnivorous plants is the alteration of the environment. To many people, wet lands such as bogs and swamps are worthless and a waste of land. As a consequence, they often become sites for dumping trash. With the increase in the "standard of living" many of these areas have been drained for housing developments, shopping plazas, industrial complexes and for recreational activities such as golf courses. With the decrease of available land due to increased demand and cost, farmers have drained wetlands for agricultural purposes. As a consequence of these activities the water table of vast areas has been lowered, adversely affecting the carnivorous plants in those areas.

The advent of modern agricultural and forest management has resulted in the reduction of wild fires and controlled burning. Fire is necessary for the health of certain groups of carnivorous plants. In some species, such as most of those that grow in the United States, fire removes some of the detritus, the dead plant remains, and competing plants which inhibit the reproduction and growth of carnivorous plants. Wild fire is necessary to release the nutrients bound up in other plants. In Australia, for example, periodic burns are required by some Drosera plants in order to flower. Others will flower more prolifically if their habitat is burned. Some seeds of Australian Drosera species will not germinate until they have been subjected to the heat or gases generated by fire.

Pollution is another factor that leads to the demise of carnivorous plant stands. The extensive use of fertilizers and pesticides produces residues which alter the habitats of carnivorous plants. Waste products from industrial processes also have an effect. Waterways in the Pine Barrens of New Jersey, U.S.A., home of several carnivorous plant species, exhibit oil slicks. One wonders what other chemicals may be dissolved in the water which are not visible.

Field collection of plants has been pushed to the foreground by many as the chief cause for the reduced numbers of some carnivorous plants. It is true that over-collec-tion is detrimental, but it is also obvious to anyone acquainted with native populations of carnivorous plants, that the plant stands often become overcrowded, resulting in substantial mortality. Judicious field collection of plants can be helpful, particularly in overcrowded stands. Wise collecting benefits the total plant population by distributing plants to other suitable habitats.

Laws have been enacted to protect this group of plants. These laws, based on sound scientific premises, have proved cumbersome and, in some situations, notably difficult to enforce.

A growing awareness for the need to preserve carnivorous plants has developed in recent years. As a consequence, many groups have been unselfishly working to preserve and manage natural bogs and wetlands inhabited by carnivorous plants. While these activities are commendable and succeed in preventing man-initiated change, the path of nature is plant succession which means that eventually wetlands will become dry land. We may be able to slow down this natural process but it's doubtful that we can stop it.

Preservation of carnivorous plants for the long-term enjoyment, thousands of years hence, will have to be by means of cultivation by as many people as possible. It is vital that knowledge of the cultural and propagation requirements for this fascinating group of plants be accumulated and disseminated to as many interested people as possible. An ideal way to do this is to join and participate in any of the carnivorous plant societies which publish newsletters.

Another unexplored potential for preserving the plants for the future is to carry on breeding programs to produce carnivorous plants that will grow in less demanding or restrictive environments.

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