Carnivorous Pitcher Plants and Their Prey

By Dr. Larry Mellichamp

UNC Charlotte Biology Dept and Botanical Gardens

Outline text based on talk given Sept 20, 2001 at UNC Charlotte,  to be broadcast on local Cable 22 Television

What are Carnivorous Plants (CP)

A.     CP are interesting plants found around the world and known for centuries for their curious behavior.  They have been widely grown as horticultural wonders. (P1)

B.     Most plants are eaten by insects and other animals for food

C.     CP are plants with leaves modified into traps for catching prey. (P2)

D.     It is a myth to think that CP use their flowers to trap prey, as depicted in comic books, novels, and stories of “lost lands” and strange places. (P3)

E.      They “turn-the-tables” – they lure, catch, digest and absorb insects and other small prey

F.      Some plants may do one or more of these things, but true cp must do all four

1.      for example, many plants have sticky hairs on their stems, leaves, or flowers – to trap would-be herbivores; but they do not digest the caught insects as in the case of this Roridula from South Africa. (P4)

2.      some plants trap insects in their leaves or flowers, such as the Jack-in-the-pulpit inflorescence (P5),  water lily flower (P6), or Dutchman’s-pipe flower (P7) – and the insects may die there – but the plants don’t digest them or absorb nutrients

There are over 600 species of Carnivorous Plants around the world – found on every continent – in order of decreasing diversity

A.     North America

B.     Central and South America

C.     Australia

D.     Malaysia

E.      South Africa

F.      Eurasia – Japan – India

Habitat and behavior

A.     they typically grow in sunny, moist, nutrient-poor soils, often associated with frequent fire

B.     They can grow in nutrient–poor sites, and thereby avoid competition from other plants,

C.     by supplementing their nutritional needs with insect prey

D.     studies have shown that they especially take phosphorous from their prey

Here in eastern North Carolina are more different kinds of Carnivorous Plants than anywhere else in the world!

A.     Centered on the Green Swamp Nature Preserve in Brunswick Co

B.     Wet meadows called savannas, and longleaf pinelands – these burn periodically

Types of Carnivorous Plants

A.     The Venus’-flytrap – is the most famous plant in the world (Dionaea muscipula)

B.     Sundews catch insects on sticky hairs on the tentacle-like leaves  (Drosera spp.)

C.     Butterworts catch insects on slimy fly-paper-like leaves   (Pinguicula spp.)

D.     Bladderworts have showy flowers, but catch tiny aquatic prey in inflated sacks on their underwater leaves   (Utricularia spp.)

E.      Finally, the main subject of this text, the Sarracenia pitcher plants

1.      There are 10 species in the Southeast, with 6 of these in North Carolina

2.      The hollow, tubular leaves may be tall or short, up to 40 inches tall

3.      Insects are lured by nectar secreted around the mouth

4.      The lines, colors and markings of the pitcher may help lure insects

5.      Downwards pointing hairs keep insects from crawling out

6.      Hoods over the openings keep prey from flying out – and keep out rainwater in most cases (Sarracenia purpurea is the one exception – it does catch rainwater)

7.      They fall in, can’t get out, die, and are digested

8.      Sarracenias catch all types of insects and small arthropods (insects, mites, etc

9.      Some eat only ants, (Spotted PP) lured into an otherwise dark interior by translucent light windows.

10.  The pitcher are effective – see what’s found in a years catch

11.  This effective system in nature can be exploited, as are similar systems - Frog in mouth, looking for a meal – steals from the pitcher plant.

As interesting as they are, the SE North American pitcher plants have not been studied very much.

A.     for example, it wasn’t until 1989 that a student of mine, Randy Salter, discovered that the numerous stamens in the flower developed from an ring of 10 initial stamen bumps.  The study was done to help determine whether the Sarraceniaceae were more related to families in the Dillenidae or the Rosidae subclasses (see Cronquist, 1968), based on direction of stamen maturation.  The question is still unresolved.

B.     There has been only one published study of pollination, by Dr Donald Schnell in 1975.  More about this later.

C.     Botanically and horticulturally, pitcher plants are interesting because they hybridize freely in the wild and in cultivation, and the hybrids are fertile. This make it possible to have complex hybrid combinations. During the Victorian plant craze in the late nineteenth century, American Sarracenia hybrids were grown and prized in England and Europe.

D.     In 1981, undergraduate students Johnny Randall , Dianne Tolman and Debbie Tolman studied wild hybrids in Montgomery Co. NC.  They gathered data to help show that this was a case of introgressive hybridization between two species, and phenomenon rarely seen in nature.

E.      Hybrids are easy to make and grow, but they grow slowly. In the wild, it may take up to 12 years to reach blooming size (Gibson, 1980).  In cultivation, they would have to be grown faster to make them worthwhile growing to sell for a profit.

F.      In 1980, student Debbie Brown began collecting preliminary data to understand how to grow pitcher plants in the greenhouse.  We studied different soil mixes, cold treatments, light requirements, and especially fertilization effects.

G.     In August of 1985, Steve Broyles and I traveled over 1200 miles throughout southern Mississippi, Alabama and adjacent Florida looking for typical and usual wild forms of Sarracenia species that might be used in breeding work.  Steve later went on to try chemical taxonomy to try and separate the species since we found so many examples of hybrids in the wild.  He met with little success using the analysis systems available at that time, but he did do some remarkable work with milkweeds in his graduate studies.

H.     In 1994, an undergraduate student of mine, Jenny Rankin, did some nutritional studies and found that pitcher plants could be fertilized a small amount, it would not harm them, and they would grow much quicker.  We settled on ½ tablespoon per gallon of water-soluble fertilizer, any brand, and NPK formulation.

I.     This allowed me to start breeding pp, making artificial hybrids in the greenhouse and selecting outstanding ones for horticultural purposes.  Now, several of these are available in mass production from tissue culture. 

J.        One of the reason we began this was due to the realization that habitat loss was taking its toll on pitcher plants throughout their range, and we wanted to call attention to these plants and their plight, and to provide interesting horticulturally-produced species to remove pressure to collect from thew wild.

K.       I have in collaboration with colleague Rob Gardner at the North Carolina Botanical Garden at UNC Chapel Hill since 1985 to make hybrids.  Some of our best named cultivars are  ‘Ladies-in-waiting’, ‘Dixie Lace’, and ‘Mardi Gras’.  One has just been patented, the first patented pitcher plant.  Redbug.

L.    Grow in various containers, tubs, pools, bog gardens.  These are now making their way into newer books on bog gardening (Glattstein, Home Gardening, Savage Garden)

M.      Also, their have been very few studies on Pitcher Plant Prey.  Mark Catesbey, the first great naturalist to come to America in 1712 and paint pitcher plants (among other native plants and animals) wrote that they were designed as places for frogs to seek shelter from the hot sun. Even Charles Darwin, who wrote a very famous book on Insectivorous Plants about 1875 never believed that Pitcher Plants were truly carnivorous.  Ironically, it wasn’t until 1875, when an ancestor of mine, Dr Joseph Mellichamp of se South Carolina published the first definitive proof that pitcher plants digested insects. 

N.   One of the most recent studies, in 1999,  was by another undergraduate of mine, Andy Baldwin, along with the help of Professor Ed Menhinick, an entomologist at UNC Charlotte.  Andy looked into (literally) hundreds of Yellow Pitcher Plants (Sarracenia flava)to see what they had caught.  In addition to finding a new species of microscopic animal called a rotifer, and an unknown slime mold, he found some interesting things about pitcher plant prey.

O.    Attract nectar eaters early

P.    Then, as dead insects start to decompose, carrion feeder come,  They too become victims.  Then, ambush bugs and other hunting insects join the fray to see what they can catch.  All in all, pitcher plants collect a hearty meal from all this eat-and-be-eaten activity throughout the growing season.

Q.      He also found that bees were attracted to the pitcher early in the season, and wasps came later in the year.

R.    In the fall, some species send up pitchers that look like flowers, and attract almost exclusively moths to their pitchers.  We still know very little about the feeding preferences of the various species of pitcher plants in the wild.  Might be something worth looking into.

Finally, the problem of pitcher plants and their pollinators. 

A.     Problem - How keep from catching the very most important insects in your life – the pollinators.  Bumblebees.

B.     Bumblebees are strong, can get out through holes they chew in the pitcher walls.  But many also become victims.  Not always good from a reproductive standpoint.  Somewhat like shooting the mailman – or killing the delivery boy

C.     One question that I have been asking, but have not been able to study in the wild, is the hypothesis  - have pitcher plants evolved a mechanism to prevent destruction of pollinating insects, at least during the time that pollination of the flowers is taking paces?  I guess it’s all right to eat the occasional bumblebee later if one happens to fall in the pitcher.

D.     Situations –

E.      S. purpurea - short pitchers, tall flowers same time – no problem.  Separation in space.

F.      S. flava - tall pitcher, tall flowers.   Pitchers not open when flowers open.  No problem.

G.     S. psittacina - Short pitcher, short flowers.– eats ants only  No problem

H.     S. leucophylla – tall pitchers, tall flowers, pitchers specialized to catch moths (we don’t know how).  No problem.

I.        S. minor – Tall flowers, tall pitchers at the same time – specialize, eat only ants – closed mouth.  No problem.

J.       S. alabamensis. – Tall flowers, tall pitchers at same time, but spring pitchers bend over.  Is this to keep them out of the way of the pollinators?  Hypotheses to study.

K.    In virtually every case, nature has provided for solution to the problem by specializing or separating the pitchers and flowers in time or space.

Conclusion –

A.     Carnivorous Plants will continue to fascinate scientists and laypersons.  Their unique behavior will provide interesting subjects for research and enjoyment.  

B.     I hope we will come to understand them better and appreciate them so as to provide habitats for them for our children to enjoy well into the future. 

C.     They are a national treasure, unique to eastern North America.  We need to do more research on them