My sincere thanks to my mentor noted aroid botanist Dr. Thomas B. Croat Ph.D., P.A. Schulze Curator of Botany of the Missouri Botanical Garden in St. Louis, MO., aroid expert and friend Leland Miyano in Hawaii, my friend and aroid expert Julius Boos in West Palm Beach, FL and friend Joep Moonen (yupe or jupe) who is a highly noted naturalist and discoverer of many plant species in French Guiana.  I love to read their notes, journals, texts, virtually daily emails and listen to their advice in person.  But there is also one other who assists a great deal: plant collector Russ Hammer in Central Florida who makes me prove what I am attempting to explain and do it clearly.  Russ often edits what I write!  Hopefully I did eventually come to the point where anyone can understand this valuable scientific principle regarding natural changes both in the morphogenesis and long term natural variation within plant species. especially aroids!  

Text complied by Steve Lucas, www.ExoticRainforest.com

Is it natural variation or morphogenesis
that causes the leaves to appear different within the same plant species?
Every leaf does not have to look alike!

The topic of natural plant variation is often a difficult concept for plant collectors.  Many simply refuse to believe that a plant species can have more than one leaf form.  Science has known the facts of natural variation within plant species for hundreds of years and it has been the topic of some very hot debates, especially in the early 19th century.  Natural variation within a species is however a well known scientific subject and is written about frequently in scientific literature and journals.  You can easily locate scientific articles on the internet.  Even Charles Darwin (1809 -1882) made a study of variation within plant species during his five year voyage around the world and published his findings in 1859. Whether you accept his theory of evolution is immaterial.  Natural variation is proven botanical science. 

It has been estimated that as many as one out of every eight plant species known to science is variable.  According to a study by Purdue University scientists are closer to identifying the gene responsible for high sodium levels in some naturally occurring plant populations and that study may have applications for further understanding a wide variety of properties which may include natural variation. 

Since this website deals primarily with members of the family Araceae which includes all aroids including Philodendron, Anthurium, etc., the discussion here will concentrate on species within that group.  But the problem that occurs within the world of plant collectors is many simply don't understand or accept the science of variation as it occurs in numerous plant species.  Variation is not limited to aroids.  You can find it in a large number of plant species, commonly in those that are tropical.  Tropical plants now include a huge number of specimens that are kept as "house plants". 

Plants simply vary in their leaf and other plant structures!  If you have more than just a few plants in your personal collection it is highly likely you possess some that are natural variations of the same plant species.  I'd be willing to bet you are calling some of them by different scientific names (assuming of course you have attempted to learn their scientific names) but to a botanist they are one and the same!   This page shows photographic evidence of the variation within collection grown and wild Philodendron species photographed in nature.  And the differences can be very confusing.

We often call the changes that occur during the life of a plant morphogenesis, the changes seen as a specimen grows from a juvenile to an adult.  The scientific name for the "morphing" process is ontogeny.  Think of it as the life of a child.  As children grow they constantly change in appearance.  If you just look at your own childhood photos or those of your grown children you are looking at those changes in appearance.  But there is another change within a number of aroid and other plant genera that is much slower, but still constant.  That change is natural variation within a species.  It occurs over a very long term which can easily be eons.  The effects of long term variation on a plant species is greatly misunderstood and has created a great deal of confusion and controversy, particularly among collectors regarding  species and their names.  But the ontogeny of a plant as it grows is also not well understood by plant collectors.   This link will help you to see the see the morphogenesis of Philodendron atabapoense

Confusing?  Perhaps I can help you to understand the dilemma of natural variation brought upon botanical scientists all by themselves as well as the process on ontogeny.  Before I offer an explanation regarding natural variation, consider this quote from my friend Leland Miyano.  Leland spent a great deal of time working and studying with legendary plant collector Roberto Burle-Marx in Brazil.  His extensive field work in South America makes him one of the most qualified people in the aroid community I personally know.  Leland explains, "I think it is best to explain variation within a species as it relates to populations, distribution and genetic exchange. If you have two widely separated populations of the same species that have not been exchanging genes for a very long time, the two populations may look very different from each other.  Sometimes the distance itself may not be great if there is a physical or other barrier to cross pollination.  If one of the populations have an extreme form, then this trait may impact the characteristics of that population.  Normally, if there are intergrades or intermediates of forms from one extreme to another, only one species is involved.   With regard to collectors, there is collection bias in the field.  By that I mean the variations that are most attractive or different are often selected from populations for introduction into cultivation.  The other bias in this regard happens due to ease of collecting area.  For example, when a new logging road is cut and only the plants easily collected near the road are obtained.  These selections may or may not be characteristic of the species as a whole and may in fact be extreme forms."

As you can easily understand from Leland's very clear explanation, field collectors, and thus home collectors, select the plant forms they prefer!  They don't always select the most common or natural specimens.  So what you often find available to a plant collector simply is not identical nor representative of the plants found in the natural environment.  And that is the very basis of natural variation within a species as it relates to collectors!

Have you ever wonder why when you do a species "photo search" on Google or another search engine you come up with very different appearing photos?  Sometimes that is simply because the person who posted the photo has a bad identification or has no training in science.  There is no such thing as an "internet cop".  But many times, especially if the website is scientifically verified, those photos of a single species will be dramatically different and that can be either morphology or variation within the species! 

At one time there was an unanswered question on a popular garden website asking for the correct scientific name for a Philodendron specimen.  The last time I checked, people were guessing a hybrid known as "Florida Beauty" and one or two other names.  Although I' tried to direct some to the correct name, simply because the plant in the garden site photo did not "look" like any photo on this or other websites that make an effort to verify scientific names, only one individual had offered the correct identification!  It did not appear the grower accepted his suggestion.

To date I've had three of the best including Dr. Croat confirm the correct identity which is Philodendron pedatum.  The photo to the left above is a juvenile specimen of Philodendron pedatum.  But the photos by naturalist Joep Moonen (yupe or jupe) at the right are also Philodendron pedatum photographed in the rain forests of French Guiana and look little like the juvenile form!  The difference in the juvenile and the adult is known as oncology or morphogenesis while the difference in the adult specimens is natural variation.  But since the photo on the garden site is neither a juvenile nor an adult and is not a perfect match to a known photograph found in a verified plant collection people just find it difficult to accept the correct scientific name!  Correct identifications are made by comparing many features found within a specimen to known specimens, not a single photograph.  And that too is the crux of understanding natural variation within the world of plant collectors!  Once you complete this article try an experiment by doing a photo search on Google and typing in "Philodendron pedatum".

I sometimes receive mail individuals who attempt to tell me the concept of natural variation is crazy and they know for certain the scientific plant names they are using are correct.  I regret to tell you, sometimes they are not!  Many are simply using a "synonym" of the same plant species.  And Philodendron pedatum has a large number of synonym names including Philodendron quericifolium, Philodendron laciniatum, Philodendron amazonicum, Philodendron laciniosum, and Philodendron polypodioides.  Many plants have 20 or more known synonym names (same plant, other name), so I'm going to attempt to use commonly grown and collected species to explain natural variation.  Some of are not going to wish to accept this as science but it is both known and accepted botanical science!

Almost every single plant in the world has at least one synonym.  So what is a synonym?  When a plant is correctly identified to science it is given a scientific name and a technical description published in a scientific journal.  If the identification is correct to the genus of the species that name becomes a basionym or base name.  But even those plants can still have a "basionym" that is wrong as to genus.  Here's an example:  In the world of aroids any aroid was originally identified in the genus Arum.  When the Linnaean system was devised hundreds of years ago there were few genera for aroids.  In the 1700 and early 1800's all botanists thought the only genus name for an aroid was Arum so every plant went into that genus.  But as botany progressed many botanists of the era began to learn there were many genera that contain aroids.  So plants such as Arum hederaceum became correctly Philodendron hederaceum.  The same has happened with Anthurium species, Xanthosoma species and many others.  Botanists simply began to understand the world of aroids was much larger than originally suspected.   

Some collectors don't like the concept of "variation" and more than once I've found internet posts or received mail which insists a plant is something other than what it is now known to be accepted in science because that collector "read" the wrong name in a non-scientific or inaccurate text.  I won't name the forum, but one often has just such discussions!  Regrettably, two of the texts, which can be  great learning tools, the very popular plant guides Tropica and Exotica by Mr. A. B. Graf, appear to be the source of much of this confusion.  Mr. Graf did a wonderful thing by introducing us to the world of tropical plant species but he was not a botanist!  He was a horticulturist and his texts are filled with errors as to the correct species name.  Many are simply made up and do not exist in science. 

If you love Mr. Graf's books, use them.  But also understand they have many errors and you must do further research before instantly accepting the names Mr. Graf offers.  I am not certain why but the current publishers of his books refuse to change anything he wrote and simply do not update his texts to make them current with the world of today's botanical science.  I spent years chasing a Philodendron he called Philodendron mandaianum.  That name simply does not exist in the world of science!  You cannot verify that name on either TROPICOS (Missouri Botanical Garden) or the International Plant Names Index (IPNI) which is a work of the Royal Botanic Garden Kew in London.   But it is in his books! 

One lady tried for months to convince me she had found a "rare" Philodendron she was calling Philodendron barryii.  She insisted that plant was so rare botanists didn't even know it existed.  My question?  Where did it come by a "botanical" name if a botanist never described the plant?  What she had "found" was nothing more than a juvenile form of another known species.  That story repeats itself constantly within the world of plant collectors!  Just try looking up Philodendron wilsonii on any scientific source!  The real name is Philodendron subincisum but a Florida grower gave it his own name many years ago!  The name he used is now accepted all over South Florida but has never been a scientifically valid name!  The confusion almost always comes from collectors, not science!

I recently attempted to learn the species name of a still moderately juvenile plant within my personal collection and I received several responses.  However, although everyone was attempting to help, one answer appeared to be wrong.  Why?  One suggestion was the plant was a variation of Philodendron hederaceum but by examining the plant I could determine that was not likely possible.  Philodendron hederaceum produces new leaves from a sheath known as a cataphyll.  My plant does not.  P. hederaceum has short petioles.  This plant does not.  P. hederaceum has a vein that runs towards the bottom of the leaf, and is a scandent climber growing close to the host tree.  My plant has none of these features other than it grows somewhat close to the host.  The petioles of my plant are very long, at least 25cm (9.8 inches)  My plant has every vein running at a 45 degree angle downward toward the side of the blade and it has more than double the leaf veins of P. hederaceum.  There are significant other features that cannot be confirmed in the scientific description of P. hederaceum.  As a result, at least in the eyes of this non-botanically trained collector, it cannot be the species P. hederaceum.  So what is it?  I simply do not yet know! 

But Philodendron hederaceum does have many variations and is the source of great confusion within the world of collectors.  Collectors prefer to call it Philodendron scandens, Philodendron micans, Philodendron miduhoi or one of many other names, possibly a dozen or more!  But those names are only synonym names of the species Philodendron hederaceum!  Collectors just don't accept that fact and continue to apply their own ideas as to which is P. scandens or P. micans or even a cultivar known as Philodendron 'Brasil' (sometimes Philodendron 'Brazil').  But they refuse to call it Philodendron hederaceum as if the name was a disease.  Collectors tend to believe if it is to be a "micans" it must have velvet leaves with a distinct heart shaped leaf blade and remain small.  Do you know in a rain forest that plant can grow to 48cm (19 inches)?  Do you know it can lose that velvet sheen?  Do you know the shape of the leaf blade can totally change?  That is the world of natural variation and the morphogenesis within a species!   And even more important, did you realize leaf size means nothing when attempting to determine the correct species?  One of the first lessons Dr. Croat ever taught me was size has nothing to do with the species!

The discussion among botanical scientists about natural variation goes back close to 180 years.  It is a very old discussion that is still argued mostly by plant collectors today.  Collectors just don't like the idea of variation.  In the scientific description of Philodendron hederaceum you'll find it has a scandent (close climbing) habit, short petioles, long internodes, deciduous cataphylls which fall from the plant along with a solitary inflorescence with normally green spathes that are reddish to purplish on the inside.  Many collectors have never even observed an inflorescence (spathe and spadix) and therefore have little scientific information to even attempt an accurate identification.  An inflorescence is the reproductive organ of any aroid and is often called a "flower" but it is not!  Instead it is simply a modified leaf!   A cataphyll is the sheath that surrounds a newly developing leaf blade.  And in nature the species does not particularly enjoy low light, the exact way collectors always want to grow it!  Instead it climbs any tree trying to reach the sun!

My personal mentor and friend Dr. Thomas B. Croat of the Missouri Botanical Garden in St. Louis, MO. once explained if you were to make collections of the species Philodendron hederaceum throughout its natural range, which is quite large and includes Mexico, all of Central America, all of tropical South America and some of the Caribbean, you would find countless slight natural variations within the species.  But all those hundreds, possibly thousands of variations, have never been granted their own exclusive name.  Only a select few which to a botanist somehow appeared distinct enough were granted such a scientific designation as Philodendron micans or Philodendron scandens.  But the names that have stuck are extremely well entrenched in the minds of plant collectors.  As Dr. Croat explained, these natural changes are simply the nature of plant evolution. 

A very interesting quote can be found within Dr. Croat's and Monica Carlsen's Taxonomic Revision of the Section Semaeophyllium in regard to one select group of unusual tri-lobed Anthurium species.  That quote states, "Size of any morphological structure in Anthurium is highly variable because plants often change remarkably in size over the course of their lives and also in response to the general climatic conditions where they occur, particularly in geographically widespread species.  Habit, Stem, and Cataphylls".  As a result, the size of the leaf, the size of the spathe, the size of almost any feature of any aroid can be variable!  To determine a species requires a total examination of the specimen and a comparison of all parts to known previously examined material!

But natural variation does not only happen within Philodendron species.  Attached are some examples of the species Colocasia esculenta, one of the most variable aroids on our planet cultivated as a food source for over 10,000 years!  These possess  hundreds of faces although they appear to be different plant species.  Still, they are all Colocasia esculenta.  You can read about that species here:  http://www.exoticrainforest.com/Colocasia%20esculenta%20large%20pc.html  And these aroids are good to eat!

Here is one possible way to understand variation within a species.  There is only a single species of human being known s Homo sapiens with many faces and body shapes.  Within the rain forest  world of plants there are many "faces" and shapes on a single species.  And that is natural variation, a concept botanists now quickly understand and accept.  It was perhaps only the botanists of previous eras who often granted different scientific names to a large number of plants that did not "appear" to be the same.  But when it comes to the careful examination of each one of those "species" they all have the same scientific features, especially the sexual features found within the spadix.  The spadix is the "post like" structure at the center of the inflorescence and is where the seeds will form if that plant is pollinated.  And that forces a well studied botanist to disregard all the newer names and revert solely to the basionym name which is correct to genus: the base species name. 

The reason?  Within the rules of botany it is well established that the very first name ever granted to a species becomes the basionym.  But that basionym is subject to change if the first genus proves to be incorrect.  Then the new first name correct to genus becomes the accepted basionym and all attempts to rename that plant simply become synonyms (same plant, other name) of the accepted basionym once all genus errors are discovered and corrected.   As a result, all the commonly used names for Philodendron hederaceum known by collectors are now simply synonyms of the base species and are no longer used within science.  They are still occasionally found, but correctly no longer the prime species' name. 

Here is one example of how variation has become one argument which continues today.  Botanist Heinrich Wilhelm Schott (1794 to 1865) understood the problem of variation within species.  He had already transferred Arum hederaceum to the genus Philodendron in 1829.  In 1856 Schott also placed Philodendron hederaceum into synonymy under his newly described Philodendron jacquinii. which is a unique species and not a synonym.  However, he included P. hederaceum in his grex Macrobelium while placing other synonyms of P. hederaceum within his grex Solenosterigma.  The names transferred along with the first were Philodendron scandens, Philodendron oxycardium, Philodendron micans and others.  But the discussion on the correct scientific name for this species had begun.  But still today, almost 180 years later, plant collectors prefer not to accept those changes.  It appears that may be largely due to the texts Tropica and Exotica.

In 1899 botanist Gustav Heinrich Adolf Engler (1844 to 1930) treated the species science now accepts as Philodendron hederaceum as four distinct species which included Philodendron scandens, P. oxycardium, P. micans and a name no longer used.  And the debate was now well underway.  This quote can be found in a treatment on this subject by Dr. Croat, "Both Engler and Krause erred in treating Arum hederaceum Jacq. as a questionable synonym of P. hoffmannii (= P. jacquinii), citing Jacquin's (1763) t. 152 as the type.  Despite the confusion by Engler and Krause, Standley and Steyermark (1958b), in the Flora of Guatemala, correctly dealt with the taxonomy of P. hederaceum, citing P. scandens, P. oxycardium and P. miduhoi in synonymy there under. Their treatment of P. jacquinii was incorrect, since they cited that name under the later synonym P. hoffmannii Schott (1858).  In this regard they followed Krause (1913).  Thus, despite the confusion by Engler and by Krause, the nomenclature of these species was essentially rectified as early as 1958, to the species as P. oxycardium or P. cordatum hort. (non Vell.)."  Despite that confusion, botanist Julian Alfred Steyermark (1909 to 1988) correctly dealt with the taxonomy of P. hederaceum in 1958 citing P. scandens, P. oxycardium and P. miduhoi as synonyms of Philodendron hederaceum.   But then in 1963 botanist George Bunting attempted again to grant a new name to a plant that is now clearly understood to simply be Philodendron hederaceum.  Other noted botanists have written opinions all along the way about the variation within the species Philodendron hederaceum and it is now considered a settled argument with P. hederaceum being the base species name (basionym).  So the problem of incorrect multiple names for a single species has long been both debated as well as understood.  Attempts were made to correct the problem beginning many years ago and is not something recently created.  

But collectors just don't always like to accept botanical science!  Collectors appear to prefer a different name for anything that does not look alike.  And they love to believe anything they read on the internet.  Sorry, the internet is filled with fantasy and down right distortions of science!   

The scientific information within this text was taken directly from the published work of aroid botanist Dr. Tom Croat along with numerous email exchanges and visits.  A great deal of this material was contributed by aroid experts Julius Boos and Leland Miyano as well as by many other interested experts and researchers.  This text is little more than a compilation of all their collective work and input.  Some of the photo on this page were contributed by grower Brian Williams.  Other photos featured on inserted links are courtesy of grower Windy Aubrey.

Text compiled by Steve Lucas, www.ExoticRainforest.com   Please feel free to offer additional technical input.

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