Carnivorous Plants Website
Carnivorous Plants in the Wilderness
by Makoto Honda

Carnivorous Plants

Anatomy of Carnivory

2017-04-14  Under construction  ------------------  Anatomy of carnivory



For carnivory to take effect, there must be contact between leaf and prey. If a fly lands on a leaf and a moment later flies away, the contact is not sufficient. A fly must be persuaded to stay for a period during which the digestion can take place. 


The first step in the sequence of events leading to successful carnivory is a lure (visual/olfactory/food) that brings prey to physical proximity. Capture -- forced retention -- follows. Digestion then starts that decomposes the prey -- the protein in the animal's body is broken down into amino-acids. The digestion proceeds with plant's own enzyme or with the help of other commensal organisms. 


The products of digestion are absorbed into the leaf and are carried to the growth site of the plant. The main nutrients selectively absorbed by carnivorous plants are nitrogen (N) and phosphorus (P) but some other elements required in trace amounts such as potassium (K: kalium) and magnesium (Mg) are also utilized by some species.  


For various CP genera below, we present the anatomy of carnivory in four steps showing the basic mechanisms involved. 


1.  LURE 
   - visual (leaf color / leaf shape / dewy-look... UV pattern)
   - olfactory (fragrance)

   - food (nectar glands)


    - pitfall trap  (pitcher-shaped leaf / wax / hairs...)

    - adhesive trap  (adhesive glands - how many times)

    - snap trap  ()

    - suction trap  (glands water expulsion)

    - lobster-pot trap  (glands water flow / hairs)



    - digestive glands secrete enzyme - the Golgi apparatus (how many times.../how soon)

    - commensals (bacteria,,,, / commensal bugs / mutualism)


    - glands  (cuticular discontinuity)

    - no glands (cuticular discontinuity)


GLANDS - The gland plays a significant role in carnivory: Glands are used for lure (nectar gland), digestion (enzyme secretion) and absorption of the digestion products. For adhesive traps, the glands are also used for secretion of viscous mucilage (or resin in the case of Roridula). Generally, adhesive secretion can repeat many times, but can occur only once in Pinguiculas adhesive glands. Depending on the types of traps, different kinds of glands perform different functions, or the same gland assumes multiple tasks.


DIGESTION - In pitfall traps, the digestion can start in the preformulated fluids immediately upon prey capture. In other trap types, there is detection/perception of stimuli associated with prey capture, and the digestive process is initiated within a certain time frame. Also, the secretion of the digestive enzyme may repeat several times (as in Dionaea) or can occur only once (as in Pinguicula) depending on the structure of the gland (presence or absence of conducting tissues to the gland). The absorption of the products of digestion is usually carried out by the same digestive glands.     


MOVEMENT in CAPTURE - We note that in the course of adaptation to carnivory, there are two distinct points at which a physical movement was acquired, leading to so-called "active" traps in carnivorous plants. One is in the order Caryophyllales in the branch leading to Drosera -- namely the Drosera's tentacle bending (and leaf folding) that eventually led to the snap traps of Aldrovanda and Dionaea. In the same order, the branch leading to Nepenthes, Drosophyllum and Triphyophyllum did not acquire any such movement. The other is the leaf movement (curling and dishing) in Pinguicula upon prey capture that --- though not as direct or obvious a transition as in Droseraceae --- may have some connection to the workings of some aspect of Utricularia traps... 

EVOLUTION CP emerged from non-carnivores at several distinct points in evolution. They only appeared as either an adhesive or a pitfall ... and then, only adhesives moved on to more sophisticated trap mechanisms... 

a) CP emerged as pitfalls in:

b) CP emerged as adhesive traps in:
           Drosera  --- >> Snap traps (Aldrovanda/Dionaea)
                            --- >> Pitfall (Nepenthes) --- >> Adhesive again (Drosophyllum/Triphyophyllum)
           Pinguicula --- >> Suction traps (Genlisea/Utricularia)


OCCURRENCES OF STICKY-CARNIVORES  We often talk about the number of occurrences of carnivory in the course of angiosperm (flowering plant) evolution. In the order Lamiales, there appears to be multiple, independent points where adhesive-trap carnivores emerged (Philcoxia, Byblis, Ibicella/Proboscidea, Pinguicula). But there are many taxa in this order that possess glandular foliage, generally for defense purpose. These adhesive glands probably can be traced back to a very ancient common origin. Give what we do not know, once a reasonably efficient and workable gland structure has been established, creating a sticky carnivore out of a sticky defense seems a relatively small step. Therefore, even if this final step toward carnivory might have taken place independently in a handful of different families in Lamiales, considering these occurrences completely independent is a little misleading (or of little value). We should be cognizant of the fact that carnivory requires a lot of things and ground work had started long ago, probably in the common ancestors of these families. This certainly does not mean to imply that "carnivory" had been contemplated upon as a long-term goal when the gland structures were being developed eons ago and, from that point forward, having been worked on to finally come to fruition by this final step --- Evolution, by definition, does not have any "future" plan. What I am saying is that, once we understand what carnivory entails and how it might have come about, counting the number of occurrences of carnivory --- by just noting the final stage toward carnivory --- may not be as meaningful an endeavor as we might have initially thought.


ANATOMY OF CARNIVORY                                                       LURE / CAPTURE / DIGESTION / ABSORPTION  (illustrations)


Poales                 Bromeliaceae                Brocchinia

                             Eriocaulaceae                Paepalanthus


Oxalidales           Cepalotaceae                Cephlotus 


Caryophyllales    Droseraceae                  Drosera



                             Nepenthaceae                Nepenthes

                             Drosophyllaceae            Drosophyllum

                             Dioncophyllaceae          Triphyophyllum


Ericales               Roridulaceae                  Roridula

                             Sarraceniaceae             Darlingtonia




Lamiales             Plantaginaceae              Philcoxia

                             Linderniaceae                Lindernia

                             Byblidaceae                   Byblis

                             Martyniaceae                  Ibicella


                             Lentibulariaceae            Pinguicula






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