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Once I get a new plant, I like to know what kind it is. This means that I want to know the genus and species of the plant, and perhaps what variety it is. Most gardeners may not realize that this simple desire is not so easily met, even amongst scientists who specialize in the accurate identification and ancestral lineage of plants. Read on to see why this is so . . .
The Species Problem
Houston, we have a problem. . . - no, not a space problem, but a species problem. In fact, this problem has been around just about ever since scientists first attempted to classify living organisms. The concept of species is something that most of us may take for granted, but it is far from being a clear-cut concept. You'd think that the question would have been settled when Darwin wrote his book, On The Origin Of Species. The surprise is that not only has the species problem not been resolved, it has become even more convoluted over time!
As a plant breeder, I have had to be concerned with species and varieties of the plants I work with. I've tended to assume that if two plants can interbreed and produce fertile offspring, they are the same genus. However, my breeding experience does not match the classification that scientists have applied to the plants I work with. Some feel that plants of the same species can interbreed and produce fertile offspring, but to me that seems self-evident. After all, if plants of the same species cannot interbreed, than no evolution of any kind can take place! Of course, this line of thought implies that two plants which are different species cannot interbreed and produce fertile offspring. In my breeding experience, I have found this to be true in some cases and false in other cases.
The next consideration, for me, was that if you have two specimens of the same species and cross-fertilize them, the offspring should look just like the parents. If the offspring are all different, that is a clue that you are working with hybrids, not species. But consider that from the so-called ‘biological’ species concept, originally articulated by Theodosius Dobzhansky and Ernst Mayr in the 1930s and 40s, on through to current thought, you can find in the literature as many as 21 (that's twenty-one) different concepts of what a species really is! A Google search for "the species problem" yields a diversity of references and points of view on this topic and demonstrates vividly how far from consensus the scientific community is on this question.
Getting specie-fic
So does this question of what a species is really matter? After all, we just want to know what to call our plants, so why not just come up with a name for each plant and leave it at that? The reason is that this problem is the underpinning of evolutionary biology. Speciation, understood as a fundamental evolutionary process, has little meaning if we have no reliable means of differentiating between species. I present this here to point out the real difficulties faced by scientists every day when working with different types of organisms, and especially when trying to go beyond observed facts to hypotheses and theories advanced by them to explain those facts.
In my breeding work, I try, with deliberate intent, to recombine different characteristics of what may be different species in an effort to develop an entirely new or novel plant. To do so successfully, I need to find what I call a breeding pathway, a combination of plant types or species, that will allow me to advance towards my goal while continuing to yield fertile offspring. Some crosses I've done do yield interesting offspring, but they are sterile, so the pathway is a dead end. In my work with plants in the genus Alocasia; some "species" cross freely in both directions, others cross in only one direction, and some won't cross at all. Some that cross in only one direction have fertile offspring, while others that cross in only one direction have sterile offspring. So far I haven't seen enough consistency in the way crosses work to enable me to say for sure if I am working with different species or merely different varieties of the same species.
I'll provide a few examples of where the designation of species appears to fall short of being sound. Two plants I've wanted to breed with are Alocasia wentii and Alocasia hypnosa. See my previous article, Alocasia hypnosa for more information about that plant. To my dismay, I discovered that while both plants bloom, neither of them produces any pollen! So sexual reproduction is not possible in these plants. To me, sterile plants may indicate that they are the result of some hybridization attempt, either natural or artificial. This is my viewpoint because I have produced similarly sterile hybrids from my own breeding work. However, such hybrids should not be considered as new species.
So you see that the species problem is not just a question of what kind of foundation the theory of evolution is built upon, but of whether one can be successful at improving or modifying plants via hybridization.
Photo credit: LariAnn Garner
About LariAnn Garner
LariAnn has been gardening and working with plants since her teenage years growing up in Maryland. Her intense interest in plants led her to college at the University of Florida, where she obtained her Bachelor's degree in Botany and Master of Agriculture in Plant Physiology. In the late 1970s she began hybridizing Alocasias, and that work has expanded to Philodendrons, Anthuriums, and Caladiums as well. She lives in south Florida with her partner and son and is research director at Aroidia Research, her privately funded organization devoted to the study and breeding of new, hardier, and more interesting aroid plants.
Posted by dahlianut (from Calgary, AB) on August 26, 2008 at 1:23 PM:
Thanks LariAnn for another really great article. When I became a dahlianut I read alot of papers about dahlia species. I still don't think there is a consensus about this genus. Numbers of species range from 12 to 48 depending on the expert. Bravo for your continuing efforts to investigate and understand this. It hurts my head LOL.
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Posted by leachg (from Merritt Island, FL) on September 1, 2008 at 6:49 AM:
Interesting article but you are far too technical for me. My problem is being able to go to Wal-mart, Lowes, Home Depot or Target and being able to purchase a plant that is even identified. Don't ask the clerk, they only stock or water. I put the blame on the supplying nurseries. Supposedly, they might know the common name of the plant they are growing.
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Subject: Great
Posted by phicks (from Lakeland, FL) on August 26, 2008 at 11:41 AM:
I allways Learn New Things From reading your Articles Thanks Paul
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Subject: Always fascinating!
Posted by JaxFlaGardener (from Jacksonville, FL) on August 26, 2008 at 9:09 AM:
Thanks, LariAnn, for your very clear and concise discussion of the species problem. I, too, like to know the botanical names of my plants so that I can find common characteristics amongst them. It is sometimes perplexing to try to figure out why some plants are placed in the same genus when they seem to have not much in common -- the Jatropha genus, for instance, where there is similar flower structure amongst the species, but a wide variety of leaf shapes and other features. And frustrating, too, to finally have a botanical name for a plant committed to memory, only to find it has been reclassified into some other genus or lumped with another species.
Even with the uncertainties, though, the botanical names can provide a means of better understanding our plants and how they relate to other plants.
