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Carnivorous Plants Gilbert A. leisman THE KANSAS SCHOOL NATfJRAl/$T VoL 30 4 University Kansas Apr. 1984 2 The Kansas C 01 Naturalist Published by . mpon State Unive ity and Issued The Division of Sciences Editor: Robert F. Clarke Editorial Committee: Gilbert A. Leisman, Tom Eddy, John Parrish, John Ransom The Kansas School Naturalist is sent upon request, free of to Kansas teachers, school board members and administrators, librarians, conserva tionists, leaders, and other adults interested in nature education. Back numbers are sent free as as supply lasts. Send requests to The Kansas School Naturalist, Division of Biological Emporia State University, Kansas, 66801. The Kansas School Naturalist is published in October, December, and April of each year by State 1200 CommerEmporia, Kansas 66801. Second-class postage paid at "Statement by the Act of August 12, 1970, Section 3685, Title 34, United States showing and Circulation." The Kansas School Naturalist is published in October, December, February, and April. Editorial Office and Publication Office at 1200 Com mercial Kansas 66801. The Naturalist is edited and published by State University, , Kansas. Editor, Robert F. Division of Biological Sciences. 3 Carnivorous Plants Gilbert A. "People were and a little disgusted, to learn that the was carnivorous, and that the flies and other in the cups were by the sticky substance there. We in temperate zones were not ig norant of insectivorous plants, but we were unaccustomed to find them out side hothouses, and apt to con sider them as in some way slightly inde cent, or at least improper. But actually that the was the a triffid's stem could lash out a slender weapon ten feet of discharging long, poison to kill a man if it struck squarely on his unprotected skin ... But there were a number of not unob vious characteristics which comment for some little time. It was, for instance, quite a while before anyone drew attention to the uncanny accuracy with which they aimed their and that they almost invariably struck for the head. Nor did anyone at first take notice of their habit of lurking near their fallen victims. The reason for that became clear when it was shown that they fed upon flesh as well as upon in tendril did not have sects. The the muscular power to tear firm but it had strength enough to pull shreds from a decomposing body and lift them to the cup on its stem." The Day of the Triffids John Beynon Harris Man-eating plants? Rubbishl Science fiction? Obviouslyl Pure poppycock? There are, indeed, plants Not which are capable of digesting trapped insects, as indicated in the first sentence of the above quotation, and which can even digest other very small animals as well. In view of their somewhat varied it is more to refer to them as car nivorous rather than insectivorous. Most flowering plants, of course, carryon photosynthesis and this is usually the process for producing energy-rich compounds, like sugar. In such plants the various nutrient elements needed for metabolism are typically absorbed from the soil with water. Carnivorous plants carryon and most of them (Blad derwort is an exception) are anchored to the soil and absorb nutrients and water from the soil just as ordinary plants. Why then do carnivorous use animal as a part of their diet? Are animal proteins essential to such plants? Do these plants grow in some special type of environment that re quires a protein supplement? Questions such as these have scientists for years; even Charles in 1875, published a book entitled Insectzvorous Plants. Most of the answers to the above are probably contained in the characteristics of the habitats in which The cover illustration was prepared by Dr. R.P. Keeling, Biology, Emporia State University, and is based on an inspirational (?) sketch by the author of this article. The sketch, in turn, was in spired by a well-known TV rom chip commercial. 4. these plants grow. Typical habitats in clude acid, mineral-poor and swamps, and freshwater marshes and savannahs. The waters of such habitats are usually dark brown in color and are facilitates very acid. This acidity the leaching out from the soil of many irreplacable minerals. may also play a role in nutrient availability. Warm temperatures en courage the growth of bacteria and fungi and hasten the breakdown of organic matter to available the most of which are utilized bacteria and fungi with the remainder subject to In cool temperatures, decomposition slows down perceptably and the nutrients re main bound and unavailable. The factor in all of this is poor nutrition. The next question is which nutrients are in short supply. Since critical component of element most in short supply in soils, a great deal of attention has been focused on it. And, indeed, have confirmed adds con siderably to the of the plants. However, current research seems to in dicate that other minerals are perhaps Both have been shown to an impor tant role in the rate of absorbtion of from animal protein .. Research has also shown that car can be grown in the nivorous absence of animal protein. It has also been shown that suitable fertilizers can be supplied to the roots, leaves, and even to the traps and be ab sorbed bv the plants. However, in both cases (complete absence or artificial fer is slow, tilization) growth of the flowering and and budding is lessened. there is something in the insect or other animal that we have not identified that is essen The search for tial for optimum that elusive something is the stimulus for continuing research on these unusual plants. There are about 250,000 flowering plants on the earth. Of about 400 are known to be carnivorous. They belong to six families and 13 genera. In all cases it is the leaf that is modified to form the . With 400 different plants would seem variation in the leaf trap. there is. However. most of them share two things in common: there is some mechanism or device to secure the insect in or on the trap and there is the secre tion of enzymes to break down the animal Basically, carnivorous plants can be classified as active or passive trappers (Figure 1). 5 Fig. 1. Active (A, B) and passive (C, D) trappers among carnivorous plants. A is bladderwort which has bulbous suction traps. B is Venus' fly trap in which the halves of the leaf dose together. The pitcher plant (C) has a pool of at the bottom of the funnel-like leaf. Sundew (D) has sticky glandular hairs on its leaf surface. (From Car nivorous Plants, Y. copyright 1978 by Scientific American, Inc. All 9 7 ACTIVE TRAPPERS These are plants which employ a rapid plant movement to entrap and secure the insect. L Closing traps We have only one in the western that qualifies under this flytrap (Dz'onaea) (Figure very restricted range. being found only in the savannahs of southeastern North Carolina and northeastern South 2). Each !eaf consists like a clamshell. Around the margins are numerous rigid and pointed hairs or teeth. The upper surface of the leaf blade is covered with glands which often serve two purposes. They frequently become bright red in thus attrac insects. and also secrete digestive enzymes. Also present on the upper surface are trigger hairs, usually three per half. When two of these hairs are touched in succession (usually by an the two halves of the leaf quickly teeth intermesh, close, the 3) and the inset is trapped inside the glandular to be slowly enzymes. Once the insect is fully digested, the leaf opens up and the un digestible skeleton is blown away. 2. The only represen tative that we have of this category is the bladderwort (Utricularia). However, it IS a genus, containing some 250 and most, if not all, are car nivorous. are worldwide in distribution and, while they do grow in a variety of habitats, most are aquatic. 3. Fig. 2. Distribution map of Venus' fly trap. A. General view of Venus' plant. B. Close up of open leaf on left and closed leaf with insect trapped in side on 8 The modified leaves or traps are bulbous, very small (up to 3.0 and have a trapdoor at one end. The open ing and closing of this is quite and several of the details will be omitted here. The door is sur rounded by a ring of tactile hairs which are very sensitive in their response. Dur ing the stage, the door is closed, and much of the water inside the blad der is absorbed so that a negative pressure or suction results. If a water for were to swim along and touch the of the door would spring open inwardly, water and the flea would be sucked into the blad and the door would slam shut (Figure lA). all of this takes 1/ 460 of a second I Once in inside the bladder, the flea is slowly ~.~;~'''.'-~ by glandular enzymes secreted by the inner This fantastic speed of the bladder wort trapdoor and the rapid closure of the Venus' fly trap have been the subject of much speculation. No normal metabolic process would seem to ac count for such rapid response. Current ideas center around an electrical action potential which can trigger an instan taneous change in turgor pressure of the cells involved in the response. leaves are modified to form tubes or closed funnels with a mixture of water and (usually) enzymes forming a pool at the bottom. The prey is lured one method or another to the mouth of the pitcher, enters or falls in, and is in the pool at the bottom. The Sarracenia is by far the more common of the above two genera, being found in bogs and marshes in much of northern and eastern North America There are unfor generally tunately, they have a tendency to which makes iden tification a bit sticky especially in areas of overlapping 4. PASSIVE TRAPPERS These are plants that, for the most part, do not require any motion as part of their trapping response. Some, like the sundew, do respond, but only very slow ly, and the response is really not all that essential to the trapping process. These are the so-called 1. Pitfalls pitcher plants, including such genera as Sarracenia and Darlingtonia. Here the Distribution map of most widely distributed of pitcher plant (S. purpurea). Darlingtonia is a western genus found in the coastal bogs and mountain slopes of Oregon and northern California (Figure 5); there is only one 9 which prevents any kind of a foothold_ As a the only possible conse quence is an unwelcome in the en pool at the bottom (Figure Ie). Special glands the pool area secrete proteinaceous enzymes, and the amount of enzymes appears to be direct ly proportional to the number of prey. To make matters worse for the prey another of downward-pointing hairs is present near the bottom, ensur ing permanent entrapment. 5. Distribution map of Darl ingtonia. ---_ _--- .• The structure of Sarracenia pitcher plants is similar from to species. The tube or funnel like leaves are topped by a lid or hood. in one this hood is reflexed over the pitcher opening and may prevent the entrance of excessive rainwater. Running down the length of the outer surface of the leaf and facing the center of the cluster of leaves is a fairly wing or ala whose ex act function is not known. There are a number of adaptations to both lure and entrap prey. The pitchers are often brightly colored green, various shades of red, yellow, and white 6). The of the hood has numerous nee· taries which yield a sweet-smelling HOnce inside the opening the prey finds it virtually impossible to get out. The inside of the hood is covered with stiff downward-pointing hairs which prevent egress. Inside the pitcher itself the inner lining of the upper third or half consists of a smooth waxy cuticle 7. Darlingtonia, stalk at left. with flower 10 6. Dark veins on leaves are bright red in nature, Pitcher to attract insects. Darlingtonia are similar to those of Sarracenia except for a of features. At the top of the pitcher is a prominent hood which is reflex ed so that the opening to the pitcher faces downward. From the outside edge of the a two-lobed or forked ap pendage extends downward Viewed from the side, the whole and its looks somewhat like a coora, hence the common name cobra plant. Finally, the pitchers of Dari zngton£a twist 180 a in either direction so that they wind up away from the center of the cluster. Internally. the major difference is the glands any place in absence of the pitcher. Presumably the prey is by and the There is at least one other pitcher plant of mention since one fre quently sees it as a This is the tropH:a! plant Nepenthes. It is a vine-like growing to 50 or more feet in The vine produces long flat leaves which very drUs from their tips. In turn, the the tendrils frequently, but not produce pitchers (Figure 8). Each pit cher has a hood or lid which is usually brightly colored and covered with nec taries, undoubtedly to attract insects and other prey. The mouth of the 11 ---~"'-~~.-------------------------- Pitchers of Nepenthes borne at end of tendrils. chef has a ribbed at the base of each rib is a downward projecting tooth. Below the teeth is a smooth waxy area, and below that a with water and 1. "Flypaper" or adhesive traps Sundew (Drosera) is the best known of this group of carnivorous plants (Figure Since many sundews are small in size are frequently less than 5 em they are frequently overlooked in their habitats. The upper surfaces of the leaves are covered with numerous sticky glandular hairs which immobilize any small prey that comes in contact with them. Following 12 leaves are covered with glands, both stalked and sessile. The stalked gland is responsible for entrapment and the sessile gland for digestion link dlg~stt ...c lone, 51-lOwing gLmJs Fig. 9. section of entrapment, many of the surroundmg glandular hairs bend toward the prey and the leaf itself may fold so as to bring as many as possible in contact with the prey. This is a slow pro cess, however, and is part of digestion, not entrapment. The of course, secrete enzymes, with those in the center of the leaf being most There are about 100 and in plant is butterwort are 48 known America our species are ed to Canada (Figure southeastern coastal area of the United States (Figure 13). A typical butterwort a small rosette of flattened or slightly fleshy leaves (Figure Like the sundew, the upper surface of the Fig. 10. Distribution map of one of the northern of sundew, the roundleaf sundew (D. rotundifolia). Fig. II. Distribution map of the southeastern of sundew, the shortleaf sundew (D. 13 Fig . 12. Distribution map of nor thern species of butterwon (P. vulgaris). Fig . 13. Distribution map of south eastern coastal species of butterwort (P. pumila). Fig. 14. Rosette of leaves of butter won (Pinguicula). 14 Fig. 15. Scanning electron micrograph (SEM) of surface of butterwort leaf show ing large, stalked, entrapment glands (black arrow) and small, sessile, digestive glands (white arrow). CULTIVATION OF CARNIVOROUS PLANTS Contrary to popular belief, a majority of these plants lend themselves readily to cultivation with a minimum of time and effort. Space does not permit going into detail, but an excellent source book is Carnivorous Plants, Adrian Slack, 1979, MIT Press. Also contrary to belief, you don't have to "feed" these plants hamburger or filet mignon. Even the most fastidious of households has enough insect life to satisfy most of these plants. As a matter of fact, why pay an exterminator to come in each spring and fall to get rid of the "bugs"? Put a few carnivorous plants around the house, they'll do the job efficiently, and they won't charge even a farthingl One final word of caution. Do not collect carnivorous plants from the wild. This is important because these plants 15 play a role in a type of environment. The are not com mon, in many places they are rare, and in many states they are protected by law. Man seems to have a talent for disrupting and even destroying natural environments. And a car nivorous bog is an one. Please. let's leave this one alone. There are several nurseries that offer carnivorous plants for sale. Some are listed in the book by Slack above; others are listed in Schnell, an· notated in the reference list below. These nurseries, of course, had to start with wild plants, but all pro pagation of them has been within the A particularly propagation technique that is us ed today is tissue culture. This is a clon ing in which small bits of tissue from a parent plant are induced to grow into completely new mature plants, all just like the parent. Venus' flytra p is to this technique, which accounts for its frequent appearance in stores as a novelty OTHER SELECTED REFERENCES Yolande. 1978. Carnivorous Plants. Scientific American 238: 104-115. Lloyd, F.E. Carnivorous Plants. Dover Books. Mellichamp, T. Lawrence. 1983. Cobras of the Pacific Northwest. Natural April issue: 46-51. Schnell, Donald E. 1976. Carnivorous Plants of the United States and Canada. Blair, Publisher. Kansas School Naturalist Emporia State University 1200 Commercial Street Emporia, Kansas 66801 Entered as Second Class Mail and Second Class Postage Paid at Emporia , Kansas