Note: This manuscript was accepted as a guest editorial by American Biology Teacher Editor Randy Moore in November, 2002. It was later rejected by the Managing Editor, who claimed that it was no longer timely because she had delayed publication due to her neglect. The Plant Science Bulletin editor was nice enough to publish it in 2005.

Here's what the Editor, Marsh Sundberg, said in his introduction to the issue:

"In the second article of this issue I summarize what appears to be a standardized syllabus for introductory botany courses around the country, based on syllabi submitted by members following a call for contributions last year. You may or may not be surprised by the results but to me it's a wakening call that is at least partially addressed by David Hershey in his lead article. There are certainly stereotypes about plants, widespread among biology teachers, that we do not do a good job of addressing. One approach is to confront these stereotypes head on with alternative viewpoints and documented examples. David provides some interesting examples that can certainly be incorporated into our introductory botany courses (if we are willing to make a place for them)."

Hershey, D.R. 2005. Plants are indeed intelligent. Plant Science Bulletin 51: 75-77.

Plants Are Indeed Intelligent

Biology Today columnist Maura Flannery (2002) rejected Anthony Trewavas (2002) thesis that plants have intelligence mainly by assuming it was merely an "animal metaphor". However, Trewavas (2002, 2003) was not being metaphorical, he was being literal. Flannery (2002) arbitrarily restricted the term intelligence to "an animal way of doing things." However, Webster's dictionaries don't restrict intelligence to animals.

Webster's dictionaries define intelligence as "the ability to cope with a new situation" (Agnes 2002) or "the ability to learn or understand or to deal with new or trying situations" (Woolf 1973). Flannery (2002) described how plants cope with new or trying situations such as high temperatures, water deprivation, and attacks by herbivores and pathogens. Therefore, no "animal metaphor" is required. Plants literally fit a dictionary definition of intelligence. Trewavas (2002) said effectively the same thing as Webster; plants are intelligent because they have "adaptively variable behavior." Trewavas (1999) has evidence that plants learn, which also qualifies as intelligence according to the dictionary definition.

Flannery (2002) stated that all animals, "even a slug", have higher IQs than any plant. However, several plant species are intelligent enough to produce caffeine, which Flannery (2002) noted is a highly effective pesticide against slugs. Was the inventor of Velcro, George de Mestral, more intelligent than the cocklebur (Xanthium stumarium) which gave him the idea (Jacobs 1996)? Was Joseph Paxton, the designer of London's famous Crystal Palace of 1851, more intelligent than the giant waterlily (Victoria amazonica) whose leaf venation inspired his design (Carter 1985)? Are the chemists who first synthesized taxol in the laboratory more intelligent than the Pacific yew (Taxus brevifolia) which synthesized it first and provided them with the structure of taxol? Are the thousands of plant products in a supermarket just an indication of human accomplishment or do plants deserve some credit? Humans often take sole credit for accomplishments that were really made by plants. Many people do not seem to realize that "Man and all other animals are in reality guests of plants on this earth" (Karling 1956).

If the modern Plant Kingdom, consisting of bryophytes and vascular plants, was suddenly wiped out, humans would not be able to respond to the "trying situation" without mass starvation. Humans might even go extinct due to wars over, or overexploitation of, the remaining food chains anchored by algae and photosynthetic bacteria. However, if humans were suddenly wiped out, plants would actually benefit in several ways because they could recolonize all the areas occupied by buildings and paving and would no longer have the destructive effects of humans destroying their habitats, overcollecting wild plant species into extinction, introducing nonnative invasive plants, and polluting the air, water and soil. Even if all animals were wiped out, the many plant species that do not depend on animals for pollination and seed dispersal would not be negatively impacted. Even many of the plants that coevolved with animals might be able to survive without them.

Common themes in science fiction, and goals of real science, are human cloning and suspended animation for long space voyages. However, plants have used cloning and suspended animation for over 100 million years. Seeds can survive in suspended animation for decades or centuries (Shen-Miller et al. 1995). Plants have numerous cloning methods such as adventitious plantlets, apomictic seeds, bulbs, corms, fragmentation, layering, rhizomes, runners, suckers, and tubers.

Flannery (2002) noted the "problem" Trewavas (2002) was addressing as "the view of plants as passive and therefore not very interesting organisms". However, Trewavas (2002) was only dealing with the view of plants as passive. He never stated or implied that plants were "not very interesting." Given that Flannery (1999) wrote a column on plant blindness, it would have been much more desirable to have stated the problem more accurately, i.e. "Although a common misconception, it is a huge mistake to view plants as passive or uninteresting." Flannery (1999) actually dismissed the misconception of plants as uninteresting rather well when she asked "Why deprive ourselves of the joy of learning about organisms that have come up with so many fascinating strategies to deal with the challenge of life on Earth."

How can parasitic and carnivorous plants be considered passive when they are stealing energy and nutrients from other plants or murdering animals, respectively? The strangler figs (Ficus aurea and other Ficus spp.) are notorious for murdering their host trees. Plants are constantly battling each other to the death. Even seemingly harmless epiphytes are considered "nutritional pirates" who intercept mineral nutrients and effectively steal from their host trees (Benzing 1980). Plants may be stationary but their seeds or fruits may fly, float, be forcibly discharged or carried by animals to other locations. Fruits of coconut (Cocos nucifera) may float for hundreds of km in the ocean, and the fruit of the sandbox tree (Hura crepitans) explodes like a hand grenade when it dries and can forcibly discharge its seeds up to 100 m (Ray et al. 1983).

Plants also face hordes of herbivores and pathogens, resource shortages and harsh environments. It is hardly passive that plants use a multitude of mechanical and chemical weapons and ally themselves with a variety of bacteria, fungi and animals in their battle for survival. Their allies include nitrogen-fixing bacteria, mycorrhizal fungi, animal pollinators, animal seed dispersers, fungal and bacterial endophytes and even ants that serve as live-in bodyguards. Plants not only communicate with other plants, they communicate with their allies. For example, an Acacia tree produces a chemical in its flowers that tells its ant bodyguards not to attack the insect pollinators that visit the flowers (Ghazoul 2001).

The sizzling sex life of plants is hardly passive either. Plants flaunt their sex organs and often advertise them with flashy petals or bracts, delicious fragrances or a horrible stench. Some flowers even generate heat to attract pollinators or better disperse floral scents (Seymour 1997). Jack-in-the-pulpit (Arisaema triphyllum) changes its sex depending on the resources available (Policansky 1987). Plants fill the air with untold trillions of pollen grains. Plants sometimes even trick animals into pollinating their flowers or dispersing their seeds without giving them the expected rewards.

Contrary to Flannery (2002), I think it is a fundamental requirement that students be able to contrast animal and plant strategies to deal with basic challenges, such as energy accumulation, environmental sensing, solid and liquid intake, gas exchange, waste disposal, internal transport, mechanical support, temperature control, defense, growth and reproduction. If students are not able to describe how plants meet these basic biological challenges, then they are suffering from plant blindness. Darley (1990) noted that plants' nutritional mode requires them to be stationary because they are "collectors and concentrators" and concluded that "If we feel animals are superior, it is only because we are animal chauvinists" (Darley 1990). Whether called animal chauvinism, plant blindness or plant neglect (Hershey 1993, 2002, Hoekstra 2000, Wandersee and Schussler 1999, 2001), the problem remains that there are many biology teachers, and thus their students, "whose familiarity with plants is little more than skin-deep" (Nichols 1919). Perhaps Trewavas (2002) discovery that plants are intelligent will make biology teachers take plants a bit more seriously.

David R. Hershey
dh321z@yahoo.com

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