Carnivorous Plants

Abstract

Carnivorous plants include some 800 plant species of various angiosperm orders and families that – by enormously different and ingenious trap mechanisms – catch small animals and subsequently digest them (insects, ants, spiders, fish fry and many others). The trap types are commonly classified by the physical characteristics of the trapping mechanisms: adhesive, pitcher, eel, snap and suction traps. Digestion takes place by a range of different enzymes (see text). Although there has been an immense progress in almost all branches of carnivorous plant research in recent years (form, function, molecular genetics, geographical distribution and fossil evidence), still there are many open problems to be solved and new ones have arisen. In addition, discussion of hypotheses sometimes diametrically opposed to each other on the origin of carnivorous plants like Utricularia has continued for more than a century now. Some species such as Pinguicula, Dionaea (the Venus flytrap), Drosera and Nepenthes are viewed to be economically and horticulturally important. Drosera has a long history in western herbal medicine.

Key Concepts

  • The history of carnivorous plant research paradigmatically demonstrates the difficulty that a radically new discovery can meet in science (plants eat animals) until eventually unanimously accepted – in the present case only after a delay of several hundred years.
  • Although the habitats of carnivorous plants are generally characterized to be low nutrient acid soils and/or correspondingly aqueous environments, there seem to be many more exceptions to this rule than usually hold true on the premise of carnivory as an absolutely necessary adaptation to ecosystems devoid of or low in minerals/nutrients, especially nitrogen and phosphorous.
  • Thus, quite unexpectedly on the strict adaptational premise, several populations and species are growing in high nutrient environments (soil and water) and occur even in alkaline areas.
  • Hundreds of noncarnivorous plant species coexist with carnivorous ones worldwide in the same areas and in the same circumstances, clearly demonstrating that carnivory in virtually all of their different environments is only one option among many others.
  • Because multiple independent origins of anatomically and physiologically very similar but complex structures appeared to be intrinsically unlikely to several authors, they tried to avoid convergence as far as possible. Nevertheless, molecular investigations have substantiated at least nine independent origins of such traits.
  • The question for the origin of the most complex and fastest of all carnivorous plant traps, that of Utricularia, has so far proved to be an ‘intractable problem for evolution’. Thus, it appears readily comprehensible why so many contradictory hypotheses have been forwarded on this topic until now (for the details, see text).
  • Further research will decide whether Behe's concept of ‘irreducible complexity’ (identifying ‘a single system composed of several well‐matched, interacting parts that contribute to the basic function, wherein the removal of any one of the parts causes the system to effectively cease functioning’) can be applied to the core system of the Utricularia trap.
  • There seems to be a never‐ending interest by the public in species such as Dionaea, Pinguicula and Nepenthes, so that hardly any larger garden centre can afford not to offer them. Hence, they are horticulturally important.
  • Carnivorous plants continue to present several of the most captivating problems for systematics and evolution.

Keywords: carnivorous plants; habitats; trap structures; evolution; convergence; modern synthesis; irreducible complexity

Figure 1. Stalked trapping glands (1) of a Drosera leaf. Once insects have touched the glistening droplets (2), each attempt to escape increases the number of attachments. Subsequently, the stalked glands bend to the centre of the leaf where the prey is digested.
Figure 2. As typical pitchers, Nepenthes (drawn according to a photograph of Schmucker and Linnemann, ) attract insects by the often brilliantly coloured ribbed rims and the nectar glands between the ribs (1). Reaching the slippery internal waxy zone (2) just below, the prey drops into the digestion fluid (3) at the base of the pitcher lumen.
Figure 3. (a) A Dionaea flytrap (redrawn according to Juniper et al.) begins to operate when a trigger hair (1) on the leaf lamina (2) is mechanically stimulated. An electric potential is transmitted to the hinge of the mid‐rib (3), inducing rapid closure. (b) In the closed state, the trapped prey is prevented from escaping by the interlocked teeth (4). (c) The trap of Dionaea muscipula: note the three trigger hairs on the lobes of the leaf lamina and the long marginal teeth which are interlocked in the closed phase. Photograph by Maret Kalda, MPI, Cologne.
Figure 4. The Genlisea trapping device (redrawn according to Pietropaolo and Pietropaolo, and several further authors by R. Slowik, considering also electron micrographs): The mouth (1) and its elongations into the two spiral arms (2) provide the entrances (3) for protozoa and small aquatic animals as nematodes or copepods. The prey is directed by detaining hairs (4) to the bulb (5), where they are finally digested. For a detailed review on form and function of the trap cf. the excellent monograph on Genlisea by Fleischmann, .
Figure 5. (a) The internal four‐armed glands (1) and the external globe‐shaped glands (2) are involved in the generation of the strong negative hydrostatic pressure in the trap of the bladderwort Utricularia (redrawn according to Lloyd, and Schmucker and Linnemann, ). When the trap is set, the door exhibiting a hinge region (3) is attached to the velum (4) on the horseshoe‐formed abutment (5). The trigger hairs (6) function as highly sensitive levers. (b) When the trigger hairs (a, b) are touched, they bend the distal part of the entrance and the door is rapidly opened (6). To ease the tensions between the negative hydrostatic pressure of the lumen and the adjoining water, both the latter and the prey are speedily sucked in.
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References

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Further Reading

Fleischmann A (2010) Bladderworts: Utricularia. In: McPherson S (ed) Carnivorous Plants and their Habitats, vol. 2, pp. 1143–1227. Poole: Redfern Natural History Productions.

Greyes N (2015) Cultivating Carnivorous Plants. North Charleston: CreateSpace Independent Platform.

Lönnig W‐E (2001) Natural selection. In: Craighead WE and Nemeroff CB (eds) The Corsini Encyclopedia of Psychology and Behavioral Sciences, 3rd edn, vol. 3, pp. 1008–1016. New York: John Wiley & Sons, Inc.

Lönnig W‐E and Saedler H (2002) Chromosome rearrangements and transposable elements. Annual Review of Genetics 36: 389–410.

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How to Cite close
Lönnig, Wolf‐Ekkehard(Apr 2016) Carnivorous Plants. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0003818.pub2]