American elms

There are elms fruiting now.  If, as you walk around the city, you look down at the pavement, or the grass, or the asphalt, you’ll see at some places papery little disks, generally less than an inch across, often quite a bit smaller – some are ciliate (they have fine hairy fringes, that is), while others have entire margins (that is, their edges are unfringed), but pretty much all of them, if the tree they come from has any hope of passing on its genes to progeny, have a seed in there.  Some have their seeds at dead center, while for others they’re positioned a bit towards the apex of the fruit, but all of them, unless their parent tree was unfortunately barren, have a seed.

These fruits are called samaras.  Samaras are fruits with wings – if you look at a maple tree, at some of them about now, the red maples for example, you’ll see another kind of samara, different from those of the elm, with these ones, those of the the maples, making the helicopters or Pinocchio noses you probably played with as a kid.  The maple samaras aren’t in the rounded and somewhat symmetrical form of the elm samara, their wing, the wing of the maple fruit, is extended in one direction, on one side of the seed, and then two are joined together to make the kind of samara that spins as it lofts towards the ground or as it is carried away to be dispersed by the wind, to new places where the seed might grow into a tree (or not).  For the maples, their wings extending outwards make for simple little machines that cause them to spin as they fly away.

For the elms, they are different.  Their samaras don’t make helicopters, their samaras are in a circular or somewhat elliptical shape, some having a notch towards the top, but all having generally a saucer shape, though sometimes uncircled and stretched in one direction to make, I guess, perhaps more of a tureen saucer than one for coffee cups, but saucer shaped nonetheless – and those samaras are all over the place now, falling to the ground beneath the elms’ spreading branches.

The ciliate samaras, the ones that are densely fringed – these rounded shaggy-margined, papery, less-than-an-inch roughly-ovals, the ones you see littering the street that look like that, these belong to the American elm.

The American elm used to be the street tree, the street tree.   Planted in long rows, in lines up and down main streets and smaller streets and all kinds of sized streets, in towns and cities across America, these plantings, they made for a beautiful effect that was somewhat architectural – the branches of the elms from opposite sidewalks meeting in the middle, forming a broad arching ceiling over the street, a covering under which horses, carriages and then ultimately automobiles traveled, and along which people walked in the shade in the summertime and under naked branches in the winter.  This was the tree of America’s streets.

The American elm was also treasured for open plantings.  With its broadly spreading branches zigzagging around and angling outward like the sides of an opening vase, this elm made for a striking shape, standing tall in a yard or park, or in the National Mall in Washington, DC, or in Harvard Yard in Cambridge, MA, or in Rittenhouse Square in Philadelphia, PA, and in places of prominence elsewhere as well.

Put simply, and to quote Andrew Jackson Downing’s Treatise on the Theory and Practice of Landscape Gardening (1841), “Let us now claim for the elm the epithets graceful and elegant.”

The elm was everywhere.  And it had always been common here.  Peter Kalm, the Scandinavian botanist who explored the new world in the late 1740s, writes of this tree as being found throughout the area in and around Philadelphia and New Jersey:

“June the 28th [1749].  The American Elm, (Ulmus Americana Linn.) grows in abundance, in the forests hereabouts.”

And back then as it is now, they flowered about this time of the year, late March:

“March the 21st [1749].  The red maple (Acer rubrum) and the American elm (Ulmus Americana) began to flower at present; and some of the latter were already in full blossom.”

[the above quotes are from John Reinhold Forster’s translation of Kalm’s “Travels into North America”, published in 1771]

And, in the city of Philadelphia, in what is now Independence Square, but was at the time called the State House Square, in the 1780s Samuel Vaughan, the man responsible for designing that square’s landscape, just after the American Revolution, was given a hundred American elms by Captain George Morgan of Princeton.  Vaughan planted them in a double allee along the main north-south path, and the founding fathers of the United States would have walked among them as they worked and lived, in their day to day lives and quotidian workdays that created much of what we live within today.

And so, from the early days of European colonization through to the constructions of the cities and towns of 20th century America, the elm was everywhere.

Then, in 1929, the Dutch elm disease arrived.  First found in Ohio, within a decade it had spread to Indiana, to Maryland, to Virginia – as far as eastern Connecticut and New York City, it had spread hundreds of miles within just ten years, according to Joseph Horace Faull, professor of forest pathology at Harvard (he spent most of his time among the trees at the Arnold Arboretum in Boston), who wrote about and studied this disease, in the 1930s.

Throughout the middle and the latter part of the 20th century, Dutch elm disease spread and spread, wiping out graceful elm plantings in yards and parks and open greens, and caving in the arched vaults formed by elms’ branches across the streets of America. The distribution of the disease rapidly became coterminous with that of susceptible elms – slippery elms (Ulmus rubra), another elm native to North America, can also catch the disease, as can the English elms (Ulmus procera) that had come over to the US from Europe.

A fungus is the causative agent of the Dutch elm disease, well two fungi, actually – Ophiostoma ulmi and Ophiostoma novo-ulmiOphiostoma ulmi, arriving in the US in the early half of the 20th century, caused the first ranging of the disease, and then the more aggressive Ophiostoma novo-ulmi came on to replace that original colonizer in later years.

The fungus spreads by two routes – either via bark beetles, who carry the fungus with them as they go from tree to tree, diving into the bark to live and breed, or via root grafts.  What are root grafts?  They’re pretty much what they sound like – when elm trees grow near to each other, as you might expect, their respective roots can come into contact.  When this happens, the roots can fuse, combining together, even down to the plant’s vascular system.  This allows the fungus to spread because it can travel through this vascular system, the plant’s water transport system, the xylem.  Though the Dutch elm disease commonly spends much of its life growing as filamentous strands (=hyphae), it can also transition to a single celled form, which we call a yeast (to a mycologist, a single celled fungus is a yeast), allowing it to cruise along the xylem like a vascular highway, up and down the tree, unimpeded by bark or air, through shoots or through roots.

And so, you can imagine what this meant for those long majestic rows of elms that were planted cheek by jowl next to each other along the streets of America.  If one instance of a bark beetle arriving brought the fungus with it, the yeast of the Dutch elm disease then rapidly went from tree to tree, by the roots subterreanean vascular system, until the allee fell like a series of arboreal dominoes.

And why exactly did these trees fall?  What is it about this disease that kills the trees?  Well, imagine if you had fungi growing in your vascular system – it would become blocked up, thereby preventing the flow of nutrients to where they need to be.  The same things happen to trees infected with this pathogen – the vascular system is blocked, causing the trees to present the diagnostic early symptom of the disease, called “flagging”, where entire branches in the tree canopy exhibit drooping leaves that yellow and brown, which is then generally followed, ultimately, by the death of the tree.

There are interventions available – removal of diseased parts, insecticides to get rid of the bark beetle, fungicides to attack the fungus, cutting of the roots to inhibit spread underground – but these are intensive and require resources, both financial and in terms of labor spent on these efforts, and so replacement of the elm is generally the more viable option.

And so, through the latter part of the 20th century, American elms have become a reduced part of our urban tree community.  But they’re still there.

There are quite a few American elms in Philadelphia – there’s a large healthy one in Dickinson Square, at Tasker and Moyamensing, and there’s one in the southeast corner of Rittenhouse Square in center city, and another at the northeast corner of 22nd and Chestnut, in front of what used to be a Swedenborgian Church, and right down the street from the College of Physicians.  And if you look in the Kaskey Memorial Garden on Penn campus in west Philadelphia, or on the grounds of Friends Hospital up in Frankford, or in front of what was Lankenau Hospital, on Corinthian Avenue just south of Girard College in north Philadelphia, if you look in these places you’ll find more of the American elms that grow here in Philadelphia.  And we have English elms, too – seven enormous ones at the Woodlands Cemetery right near Penn (two of which date to William Hamilton’s time; in 1921 those two were, respectively, 10′ 1″ and 10′ 3″ around), and at Marconi Square in south Philadelphia, right along Broad Street, on the west side of Broad, there’s one with a trunk over five feet across. (and for an interesting historical record: in John Watson’s Annals of Philadelphia and Pennsylvania in the Olden Time (1899, “enlarged, with many revisions and additions, by Willis P. Hazard”), p. 373, vol. 3, he notes after a brief mention of the balloon riot that occurred in 1819 at “Vauxhall Theater, north-east corner of Walnut and Broad streets”, that “The elm that stands on Walnut street, overhanging the street, was on old tree then.” [Vauxhall was also called Vaux Hall Gardens, and had a very open parklike aspect to it, in 1819; in the 1890s, there was still a fair bit of open space in that lot, as one can see from the 1895 map here, but by 1910 it was all pretty well covered over and the elm would have been gone])

And at Independence Hall, right behind it there, along with the enormous London planes, and nearby to some little chestnuts and not far from a Franklinia, and with dozens, hundreds, or thousands of people walking under it every day, is an enormous American elm, rising high above the square.  There are other American elms there too, five in all – in that smallish square, there are multiple elms.  One, planted in 2004, is a ‘Princeton’ cultivar, a variety that, while known and planted prior to the Dutch elm disease’s incursion into America, ended up being able to co-exist with both species of Ophiostoma and therefore ended up being planted more widely, quite widely actually.  This cultivar grows well, and the example of it that is in back of Independence Hall is strong and healthy, growing  alongside its older relative that towers above the square.  These stand as a reminder of a time when American elms were the American tree, and they are the right plant to have at this historic site – trees deep in history, that are still growing tall, even though organisms that were new to them have inalterably changed their presence in the landscape, the elms stand, and grow.

To read more about elms, including Penn Treaty elms, see here;

The Callery pear

There are white flowers blooming all over Philadelphia now.  Some of them belong to the Amelanchier, also called shadbush, or serviceberry.  Some of those white flowers are magnolias.  Some are cherries, and there are others, too, but most of the ones that you’ll see at around this time are the blooms of the Callery pear (Pyrus calleryana), with their copious flush of white and their peculiar acrid smell.

If you look closely at them, one thing that you’ll notice is that nearly every set of flowers is accompanied by its own set of leaves.  Look closely, and poke around in the inflorescence (a cluster of flowers, that is) and you’ll see that each individual flower is connected to a little stem, in a somewhat spiral arrangement, winding down the axis, or winding up it, depending on which direction you go.  Each one of those flowers is accompanied by a little tiny leaf, or a leaf scar to show where a leaf once was – each one repeats the other, in modular form, winding around the stem, up and down the line.  Except all the way down the line.  At the lowermost position on the inflorescence, the one closest to main part of the tree, there is almost always a set of a leaves, a little tuft of green, instead of a flower.

Why are those leaves there and what are they doing?  It could be that they provide a local food source for those flowers, early on in their development – those photosynthesizing leaves harvesting energy from the sun and gathering carbon dioxide from the atmosphere, twisting the two into sugar, and shipping that sugar right to the nearby flowers, flowers that need energy to grow and to breed, these leaves open up when the flowers do, since they are in there in the bud with them, and they pop out along with the flowers, and would provide sugars just a short distance away, and at the right time. It’s expensive to ship sugar around a tree, as it takes energy to move things, and so doing it locally, right next to the inflorescence, instead of having the leaves come up some distance away and transporting the food that some distance, it would just simply be more efficient to do it closeby.  By having the leaves right next to the flowers, the source right next to the sink, this would save precious time and energy, always a valuable set of resources, but resources even more valuable in the spring, just after the trees have woken up and are drawing down their stored energy supplies, supplies that they packed away last year and have only in limited amounts.  And by having those leaves right there in the bud, good timing is assured – no need to wait for the leaves farther away to open up (which they will later) when you have your own right there in the package with you.  And so those little tufts of leaves at the bases of the inflorescences are quite likely feeding their neighboring buds and blooms.

And also, those leaves could be beneficial to the tree by drawing up water, pulling it towards the flowers, who need to drink, too.  The way that water moves up a tree is, basically, that the water evaporates from the leaves through little holes, called stomata; this evaporation draws the water up through tiny pipes, called, collectively, xylem, in a somewhat similar way to how water goes up through a straw when you draw on it as it sits in your waterglass.  In fact, you can see how this works by taking a drinking straw and putting it entirely underwater so it fills with water, then taking a piece of a cotton ball and jamming it tightly into one end of the straw and then taking the entire contraption up and out into the air.  Then, place it, cottonball end up, into a glass with more water in it, but this time with water that has a little bit of food coloring in it.  Then wait.  Or just come back later.  Either way, after a while, you’ll see the dyed water migrating up through the straw, ultimately dying the cotton ball whatever color you have chosen from your pack of food dye, that you used to stain the water in which the straw is sitting.  This illustrates, essentially, how water moves through a tree – the water evaporates from the leaf (in our experiment, that’s analogized by the cotton ball), which pulls it through the xylem (the straw, in our table top set up), which in turn pulls the water out of the soil (which is represented by the glass that holds the tinted water).  And so, if leaves are situated next to the flowers of the inflorescence, which they are in the case of the Callery pear, then they would be drawing up water, water that could be shared with the petals and the sepals, the anthers and the stigmata, the parts that are the hopes and dreams for the next generation of trees.

But whyever they are there, the fact remains that those leaves are there, and they are here and there throughout Philadelphia, along streets and in parks, pretty much in every neighborhood.

But how did they, and their accompanying trees, get here to Philadelphia?  The Callery pear tree is originally from east Asia, and since trees can’t walk, and nor can they swim, they had to have had some help in getting to North America, and their main agent of dispersal, the organism who got the seeds of the Callery pear to the new world, was Frank Meyer.

Frank Meyer was a Dutchman, and he was also a botanist.  Towards the end of the 19th century, Meyer worked as the head gardener in the experimental garden at the Amsterdam Botanical Garden, but this wasn’t enough to satisfy his yearnings for travel and his love of plants, and so he came to America in 1901, where he soon began to work for the US Department of Agriculture as a plant explorer.  One of his missions, towards the end of his career, was to collect the Callery pear.

Meyer wasn’t the discoverer of the Callery pear – that credit goes to the mid-19th century French missionary, Joseph Callery.  Nor did Meyer introduce it into cultivation – that credit goes to E. H. Wilson of the Arnold Arboretum.  However, what Meyer did was to send back bags of seeds, in 1917, from China, of the Callery pear, so that this plant could be introduced into cultivation by the USDA, thereby leading to its widespread dissemination.  Why was he told to collect and send back those seeds?  Well, at that time, the US pear industry was being decimated by fire blight, a bacterial disease, and it had been found that the Callery pear was resistant to this disease, and so could be used in breeding programs and for rootstock.  This program was quite successful, and when it was also found that the Callery pear can live under some difficult conditions, like a fair bit of drought, the Callery pear became commonly used in orchard production.  (fire blight is still a problem in pear orchards, by the way: )

And then, some decades after that initial delivery of seeds by Frank Meyer, USDA researchers in the 1950s noted that the Callery pear also had nice flowers and this, combined with its resistance to environmental stress, meant that the Callery pear was realized to be a tough and attractive street tree, and it rapidly became extremely popular, which is why we see it all over Philadelphia.  But it most likely wasn’t just the tree itself that led it to be so widely planted.  The timing of this work was probably key, also, to the widespread spread of the Callery pear.

These trees, the Callery pears, came in and replaced, in part, the American elm – the American elm was the premier tree of parks and streets and so many other landscapes throughout the US, up until the midpart of the 20th century.  Its vaselike structure, with branches growing up and out, made for tremendous arboreal arches that gracefully covered many streets in small towns, and big cities, and other places, too, until the Dutch elm disease knocked out this elm, and many others like it, taking it out of commission as the street tree of choice, requiring a replacement, many replacements actually, to fill the elm’s ample metaphorical shoes.  The Callery pear was one of those trees, and it became extremely popular starting in the 1960s as a tree for the street habitat, a niche that had been opened up by the Dutch elm disease.

If you see a row of Callery pears, what you’ll often notice (I know that I do) is that they frequently will all have a spraylike branching pattern, where the trunk will grow nice and straight up until about 4 or 5 or 6 feet or so, and then there will be a division of that upright axis, where branches will grow angled outwards, kind of like an upside down broom.  You might think that this is very thoughtful of the tree, to make such an eyepleasing design at about eye level, reminiscent of the form of the American elm.  However, plants don’t think, or at least I don’t think they do, and this shapely pattern is due to the hands of man.

If you cut the top off a tree, it generally will not die.  It will however, grow quite differently than it would if it had not been decapitated.  Branches that were formerly suppressed by hormonal signals sent out from that top leading growing tip can now grow, and they do – and sometimes all at once.   This is what happens with the Callery pear.  If the top of the tree is removed, you then get a spray like pattern to the branches that grow to replace that lost top.

And so, if you walk down a street, for example, 19th Street alongside the Academy of Natural Sciences, just below Logan Circle, you’ll see that at about shoulder height, the branches of the Callery pears begin to spread, and you’ll know that at some point in time, someone walked among those trees, cutting them at an easy height to reach, about shoulder height, to make those Callery pear branches angle like they do now, an angle reminiscent of an American elm.

People don’t plant Callery pears quite so often anymore – their branches tend to break, and there are concerns about its invasiveness.  This tree, which is one of the few major introductions of the 20th century to our street tree flora has had its time in the sun.  It was introduced, it had a population boom, and now we will see where it will go in the future, what part it will take among the street trees of Philadelphia and elsewhere.

Callery pear inflorescence, NYC Photo courtesy Joseph Wendler

Callery pear inflorescence, 27th of March 2012, NYC; Photo courtesy Joseph Wendler

Note: the Callery pears in Philadelphia are just now hitting there full bloom on the 13th of April 2014, and they are in fully bloom in NYC, too:

Manhattan-20140418-Wendler_Callery pear

Callery pear in Manhattan, 18th of April 2014; Photo courtesy Joseph Wendler

The yard of the Wagner Free Institute

The Wagner Free Institute is in the midst of Philadelphia, surrounded by houses and stores and shops, surrounded by sidewalks and asphalt streets, surrounded by walls and roofs and other constructed pieces and parts – interspersed with vacant lots and parks, yes, where plants and non-human animals do grow and roam quite freely, but overall the ecology nearby is people .  Temple University is just over to the east, the Broad Street line is about a 5 minute walk away, and people are just about everywhere, walking and talking all around.  This isn’t, perhaps, where you’d expect to find a historic landscape, and most wouldn’t look for one here.  But it’s here.

In the yard of the Wagner are some very large trees – London planes (Platanus x acerifolia, we’ll call them) and silver maples (Acer saccharinum) are the largest that are there.  They ring the yard and just from their size you can see they’ve been there for a pretty long time.  But just how long have they been there and where did they come from?

The first question, as to how old they are, is reasonably straightforward to answer.  To find out how old a tree is, you either cut it down and count its rings, or you take out a sliver of it and count the rings you’ve sampled by doing that.  The latter leaves the tree standing, so we did that for some of the trees in the Wagner yard.  And we were able to do this because plants keep their history a bit more readily than humans do.

Plants are not like people.  As we (people, that is) grow, we continually regenerate and renew our cells.  There’s turnover of bone cells and sloughing of skin, so that even though there are some parts that remain, we are a perpetual agglomeration of old and new.  Plants, however, grow by accretion – new cells are laid down on top of the old, and the old ones aren’t done away with to make way for the new.  They just get covered over and stacked upon.  And this happens in all directions – plants can grow up, down and out.  Herbaceous plants (plants that aren’t woody, that is) primarily grow up and down – they extend their axes towards the sky and via roots through the ground.  Trees and shrubs (woody plants), however, while they do grow up and down, just as herbaceous plants do, they also expand outwards, adding layers outward in ever widening concentric circles, every year adding a new ring, on top of the old, covered with the new.

And so, we can count those rings – and if we have a corer, we can do that with little harm to the tree.  A corer is a machine, a simple machine, in the sense that it simply changes the direction and magnitude of the force applied to it (the definition of a simple machine that you may or not remember from high school physics).  It has a screw tip end, a bit, that is attached to a long hollow stem.  At the far end of that long metal piece (these can be of varying lengths, by the way – we used an 18″ corer at the Wagner), is another metal piece, at a 90° angle to the stem.  This provides a grip and more importantly provides the leverage that allows one to turn the stem – to provide torque, if you will.  You turn the corer, it drives the bit into the tree, and because the stem and bit are hollow, this cuts out a long narrow piece through the tree, a core that you can then pull out of the corer, mount on another piece of wood for stability, sand down, and then count the rings that were laid down year after year by the tree.

Ned Barnard, tree corer non pareil, and I and a crew from the Wagner did some coring at the Wagner in October of 2011.  (I should say that I use the words “I” and “work” together somewhat metaphorically – Ned and the others did the vast majority of the work, as is generally the case).  We cored a silver maple and one of the London planes (since the other London planes were roughly the same size we only cored one of them) – then Ned labored over them, mounting them and sanding them, and then counted their age lines.

It turns out that both of those trees were in the range of 110 or 115 years old, and so this gave us a target date to use to search the Wagner’s records, to try to find out where these trees had come from.  And so I got to take a look at the Wagner’s old meeting reports, access to which was kindly granted by the Wagner, via Lynn Dorwaldt, librarian and archivist of the Wagner.

Since we’d dated (by coring) the silver maple and London plane in the yard to about 110 to 115 years old (with a lower bound of 110 years), I looked at the 1890s-1901 records. And it seems that the trees we cored most likely came from Meehan’s nursery, in Germantown, Philadelphia.

In the meeting report (of the Wagner) of the 3d January 1900 , there’s mention “that the actuary prepare a scheme for planting young trees”, this is followed by the report of the 7th of February 1900, which says “That the actuary be authorized to consult with Mr. Thomas Meehan as to a scheme for the treatment of the grounds around the Institute”.  This scheme was approved at the meeting of the 7th of March, 1900, and was “revised by Mr. Gridland” (as per the 7 May 1900 report).  Things moved quickly, at the turn of the last century.

In the Wagner archives, Ms. Dorwaldt found a letter from Thomas Meehan (dated 22 February 1900) where he mentions that he’s been ill and doesn’t do much day to day work with the business (the nursery, that is) anymore, but that his son’s handle that work – he also mentions that he’d help out with the landscape plan.  Meehan died in the autumn of 1901, so the Wagner yard may well be the last landscape that he worked on.

There’s a receipt from Meehan’s (dated 7 July 1900) for 12 trees – these most likely include those trees that are currently in the yard (the ones we cored, plus the other London planes).   Don Azuma, of the Wagner, and I took a look in the yard, and it looks like, from the arrangement of the trees, that there might have been 12 in the original planting (though this still requires further confirmation, I should say).  It looks like the planting would have been in three lines, to the east, west and south of the building (respectively) – there’s a depression in the soil at the southwest corner that is probably where one of the trees was, and that marks where the west and south lines of trees probably met.  There’s another depression west-adjacent to the SE tree, and that gives a good idea of what the original spacing of the planting would have been, if all the above suppositions are correct.

An additional note of interest on the Wagner yard – in 1895, the Wagner wanted to re-do their landscape and asked Frank Day to do the design.  Frank Day was an enormously successful architect of the late 19th and early 20th century, and he was also a founding member of the Philadelphia Botanical Club.

He (Day, that is) agreed to do the Wagner yard in 1895 – but I don’t see evidence that he produced it.  He was a pretty busy guy (for example, there’s a letter from him, written in the 1920s, in the archives of the Academy of Natural Sciences [access to which was generously provided by Clare Fleming, archivist of the Academy], where Day says he can’t serve on a committee because he’s too busy with his architectural work).  Clearly the Wagner had had grand plans for the yard’s plantings and design (and they also wanted a greenhouse), but those plans don’t appear to have been implemented, and there isn’t evidence that Day had further involvement in the Wagner’s landscape.

Ultimately, though, even though these majestic plans for the yard were not realized, as we know the yard was redone, with trees from Meehan’s – and this provides a useful piece of horticultural history, too.

London planes and American sycamores and Oriental planes can be difficult to differentiate from one another – this is the case now, and it was the case a hundred years ago.  And so, if we look at an old nursery catalog, for example from Meehan’s Nursery, how can we know if a tree listed as an American sycamore, or an Oriental plane, or a London plane actually is what they say they are?

Well, we can look at a tree that came from Meehan’s, one that is still growing, for example in the yard of the Wagner Free Institute, and we can identify it – if we see that it is a London plane, then that is pretty good evidence that this nursery was selling London planes when that tree was planted.  And since we know when that tree was planted, which we know from having cored it, we can say quite confidently that Meehan’s was selling London planes at that time.  And so, from the trees in the Wagner yard, we are supplied excellent evidence that trees that Meehan’s was selling at the turn of the last century were, truly, London planes.

However, Meehan’s was not listing London planes in their catalogs at that time.  A visit to the McLean Library of the Pennsylvania Horticultural Society (guided by librarian Janet Evans), and a look at their collection of Meehan’s Nursery catalogs, shows that in 1899 only Platanus orientalis (Oriental plane) is listed therein.  In their spring 1900 catalog, “Sycamore, Oriental plane” is listed, including the note “This is the European variety of our Button-ball”, and it is the only Platanus species listed.  In the fall 1900/spring 1901 catalog, both occidentalis (American sycamore, that is) and orientalis are listed – London plane, however, is not.  In that catalog, of occidentalis, Meehan’s says “This, our native plane, can hardly be distinguished from the Oriental plane when young”, implying that perhaps these two plants as listed might have been sold somewhat interchangeably at the time.  In the 1905 catalog, Meehan’s still only had orientalis and occidentalis, and the London plane was not to be seen listed in the catalog.  Even as late as 1917, Meehan’s still did not have the London plane listed (though that catalog does include Platanus orientalis)

And so, from evidence gathered in the yard of the Wagner and from these old nursery catalogs housed at PHS, it is clear that while London planes were being sold by Meehan’s, they were misidentified (or perhaps, rather, just “differently identified”), most likely as Oriental planes.

History is everywhere, and so are plants.  The two are intertwined, and even in the middle of the city they tangle together, and the one can tell us about the other, the trees can tell us what was there before, and what was there before tells us about the trees that are there today – and even though they may be layered over and it may take some digging and coring, they all have something to say, and they all can say it, if you just look.

London Planes and American Sycamores

All around Philadelphia, and in many other cities as well, the streets are lined with London Plane trees.  These trees, with their trunks of exfoliating bark making them look to be covered in military camouflage, are recognizable from a hundred yards away.  Or so I used to think, until I looked closely at the confusion and complexity that surrounds this seemingly simple and so common tree.

The London Plane is of hybrid origin – it is the offspring of two different species, the American sycamore (Platanus occidentalis) and the Oriental plane (Platanus orientalis), and it is a tree that did not exist prior to European colonization of the new world.  Before then, American sycamores and Oriental planes were kept separate by an ocean (the Atlantic if you’re going east from the US, or the Pacific if you want to go all the way around the other way), and they didn’t come together until the 17th century, when John Tradescant the Younger, a botanist and gardener (as was his father – John Tradescant the Elder, that is), came to the colonies in the early part of that century and in 1636 took the American sycamore to England.  There were also Oriental planes in England at that time (they’re originally from the more eastern parts of Europe), however though the geographic distances that had previously kept the orientalis and occidentalis separate were gone, still for some time after 1636 age differences would have maintained that separation, as it takes time for trees to grow, and to make flowers, and to shed pollen, and to make new seeds for new plants.  And so for some time these different plants, though now together after having been so long separated, would still have remained distinct from one another.

By 1700, though, east had met west.  We know this because in that year Leonard Plukenet, yet another English botanist, described an intermediate between the Platanus species that were already known (i.e., orientalis and occidentalis), and so from this we can infer that the London plane had arisen by then, an intermediate that looked like what it was, a hybrid cross of two morphologically distinct species.  How, when, where and why this happened, we do not know exactly, except that it was in England in the latter part of the 17th century (the latter part because it would have had to have been long enough after 1636 to have allowed for the seeds Tradescant brought back to have grown into seed bearing trees themselves).  Other than that, we can’t say with more detail, with any confidence at least, when this hybridization event occurred.

It also isn’t clear when this hybrid, the London plane, came to the US (or one could say semi came back to the US, since half its genetics is from the new world) and to understand why, you have to understand the plants.

London planes look quite a bit like their parent species, as you might expect, since that’s how genetics works (like begets like), and so it can be difficult to differentiate them.  This is something I learned recently – I had thought for years it was easy to tell them apart, to differentiate the London plane from the American sycamore.  But, as with so many things, I realized that the closer I looked, the more complicated it became.

There are, broadly speaking, four main characters that are useful for telling these trees apart, the London plane and the American sycamore.  Two of those characters involve the bark.  On London planes, the military camouflage appearance mentioned above, in the first paragraph, is found up and down the trunk of the tree – on American sycamores, the bark is thick and rough up most of the main trunk of the tree, only exfoliating (peeling away) further up.  And American sycamores generally have a white, and commonly bone-white, tone to the underbark that is exposed from the peeling away of the outer bark layers, while the London plane’s underbark will have a yellow or green tinge (or sometimes even a salmon orange color, as is found on a tree in Pastorius Park in Germantown, here in Philadelphia).

The leaves also differ – the leaves of both trees are lobed, and in the London plane, the center lobe is longer that it is wide, whereas the sycamore’s is generally wider than it is long.  A final character separates the two – the flowers (and then later, of course, the fruits) are borne on dangling peduncles (what we might call “stems” in normal English), and in American sycamores these are borne singly, while on the London plane they hang in twos and threes.

Something else also differentiates these trees – their habitats.  If you’re in the floodplain of a river or creek and you see a tree that looks like an American sycamore, it probably is.  If you’re on a city street, and you see a tree that looks like a London plane, it most likely is.  London planes are phenomenally sturdy street trees – they’re called “London planes” because they are and were so common throughout London, and while yes this is due to their attractiveness, it’s also because they were able to grow in the soot filled air of 19th century cities, and so became exceedingly popular, especially in London with its thick industrial era atmosphere.  Since its introduction to urban life, this tree has had times of peak interest, and times of reduced interest, as is noted in William Flemer III’s article “Island and Median-Strip Planting”, in Arnoldia [vol. 44(4), pp, 14-28 (Fall 1984)]: “The London plane tree has gone through several cycles of popularity and disapproval.  Many years ago a few nurserymen grew the trees from seed that produced great variation in habit of growth and disease resistance and this may be one cause for the disapproval.  Another may be the plane tree’s vulnerability to canker stain disease, a serious condition spread by pruning tools or other mechanical means.  The severity of the disease once led the city of Philadelphia to enact ordinances that prohibited planting the tree.”  But, I should add, even though the London plane has had its ups and downs in popularity, it still, generally, will do better in an urban environment than the American sycamore will.  This habitat differentiation is noticeable if you go to the Powell house on 5th Street in downtown Philadelphia – there is a London plane planted right next to an American sycamore.  The London plane is doing quite well, happy as can be – the sycamore, much less so.

Another habitat in which one seems to often encounter American sycamores is graveyards.  There’s an enormous sycamore in Greenwood Cemetery, in Frankford, and another one in the churchyard/graveyard of St. James the Lesser, which is up near Laurel Hill Cemetery – there’s also some planted in the Palmer Burial Ground in Fishtown, and quite a few planted in West Laurel Hill, just over the city’s border, in Bala Cynwyd; there’s also an enormous one in the Germantown Friends burial ground that you can see easily and clearly from Germantown Ave, if you’re standing just a bit west of Coulter St.; there’s also one in the Friends Meeting House yard at 4th and Arch – there used to be a cemetery there, too.  The symbolism of this makes sense, planting sycamores in Christian cemeteries.  In the gospels, e.g., in Luke 19, when Jesus is going through Jericho, Zacheus, the chief tax collector in town, climbs what is called a sycamore to see Jesus as he is walking by – Jesus sees Zacheus up in the tree and calls to him, and Zacheus then “received him joyously”, as it says in the King James Version.  Now, this tree from the bible is said to have most likely been a sycamore fig, and certainly was not the sycamore that we have in the US, but the symbolism, one might imagine, would still work and would be effective, because in a graveyard in which the dead await the return of the messiah, one would want a tree for them to climb up on Jesus’s return, so they can see him, and perhaps more importantly, be seen by him.

American sycamores can also grow to enormous size – in the early part of the 20th century, the American Genetic Association put out a call for photos of and associated data for the largest trees in America.  They published results of this in 1919, in the Journal of Heredity, and the largest tree by far was an American sycamore in Worthington, Indiana – it was 42 1/4 feet in circumference.  London planes can grow quite large, but I’m not aware of any that come close to that kind of size.

However, even though there are a number of differences between these plants, it can still be difficult to tell them apart.  Why?  Because even though the London plane is of hybrid origin, it still makes viable seeds, and those seeds are enormously variable, because they contain the genetics of both the parent species, in every combination available.  Also, the London plane can back cross with its parent species, thereby further mixing up the characters.  And so, many of the trees I see in Philadelphia that I once would have easily called “London plane”, I’ve come to notice often have a mix of the characters with those of American sycamore – and so separating them isn’t so easy.

This all helps to make it difficult to figure out when the London plane came to the US – if we find it difficult now to separate them, it’s not like it was any easier in previous decades or centuries, and trees identified as Oriental planes and American sycamores in old documents quite easily could have been misidentified London planes.  William Hamilton, owner of the Woodlands and an avid plant collector who sent numerous plants over from England in the 1780s, when he wrote to his gardener in 1785, he mentioned he had sent over 12 plants of “platanus orientalis”.  This may well have been London plane trees.  Or it might not have been.  We will most likely never know, because absent the plant itself, the name alone just doesn’t tell us for sure what it is.  This is the case for listings in numerous nursery catalogs (including Meehan’s) – Platanus orientalis, for example, may be listed for sale, but we just can’t be sure if that was what they were selling, and so tracking the movement of the London plane is difficult, if not impossible, to do.  An example of this confusion can be found in an article in the magazine “Park and Cemetery Landscape Gardening” from 1916, where, in an article enumerating “Trees for Adverse City Conditions” includes “Platanus orientalis (The Oriental or London Plane)”

And even the plant’s name is confused and confusing.  The latin name most commonly used for the London plane is Platanus x acerifolia (the “x” indicates its hybrid status), however, another valid name is Platanus x hybrida – this confusion arises because we don’t know which name, hybrida or acerifolia, came first, we don’t know which was assigned before the other.  This is important to botanical taxonomists (i.e., people who name plants) because sometimes a plant is named more than once; for example if someone thinks they’ve discovered a new species, and they describe it and name it, but it turns out that they just didn’t know that someone else had named it before, well that first name that was applied previously is the one that is supposed to be used, and not the later one. This often simplifies things because the choice is based simply and solely on date of publication of the name of the species.  However, it’s not always easy to figure that out, and this is one of those cases – while we know that both of these names for the London plane were assigned in 1805 (hybrida by Félix Brotero, a Portuguese botanist, and acerifolia by Carl Willdenow, a botanist in Berin), we don’t know exactly when within that year these names were used, and so priority is confused, and so are we.

And there are further questions of nomenclature here – due to the backcrossing with the parent species, and because plants grown from seeds that are progeny of a hybrid are not, strictly speaking, hybrids themselves, it furthermore becomes complicated as to whether or not many of the London planes we see should truly be called hybrids, and therefore include that little “x” in there.

The confusion doesn’t end there.  Due to that Brotero name, “hybrida“, one might think that the hybrid origin of the London plane was clear and understood early on, or at least by the earliest part of the 19th century.  But even this wasn’t clarified until much later, in 1919, when Augustine Henry and Margaret Flood thoughtfully marshaled the evidence – intermediate morphology that is between the two parent species, highly variable seeds that show traits of both parent species in various combinations – in a paper in the Proceedings of the Irish Royal Academy that clearly indicate that yes, the London plane is a hybrid of the trees from two continents.  So perhaps the confusion does end there, at least for that one question, and at least for now.

To read about the importance of cemeteries to urban planning, see here:

To read about some other local Platanus, see here:

To read about some other trees, see here:

The saucer magnolia

American Chestnut

American elms

“Penn treaty” elms

The Callery pear

The Caucasian zelkova

Paulownia tomentosa, the empress tree

The sophora

Fringe tree

A painting of planes by Van gogh

A painting of planes by Van Gogh

The Buist Sophora

In southwest Philadelphia, there is a tree, an extremely large tree, that was planted when this land was a nursery, many years before it became the densely populated area that it is today. On Hobson Street, between Elmwood and Buist Avenues, right across from Buist Park, this tree has stood witness to the development of packed in housing, to the consumption of the surrounding farmland, to the construction in the early 1920s of the General Electric Plant right up the street, and to the deconstruction of that plant, some seven decades later.

Bartram High School, right up the street and around the corner, didn’t exist when this tree was a sapling, and the city streets have grown up around it like a web around a bug. My father went to Bartram, in the 1950s, but because he was coming from the north (he grew up at 58th and Thomas), he wouldn’t have gone by this tree on the way to school, but he might have if he was walking over to Buist Park, which he may well have done, and so he may have seen that tree, just as I did in early March 2012, though it would’ve have been a little smaller, over a half century earlier.

This tree, Styphnolobium japonicum (though still commonly called by its former generic name, Sophora) spreads broadly across Hobson, and a sign on Buist Avenue points towards it, signalling the historic tree that was spared the ax as the land it was on transitioned from horticultural to urban.

The Buist Nursery was here.  While primarily known for his roses, Robert Buist (and his nursery, which was named Rosedale) grew as many kinds of plants as he could sell, and though he died in 1880, the nursery,  which was established in 1850 in the area where this Sophora still stands, was carried on by his son Robert, Jr. who in turn passed away on the 13th of December, 1910, a “millionaire seedsman”, as described in the New York Times.

Upon the death of Robert Sr., an appreciation of his life was published in the December 1880 issue of the Gardener’s Monthly, and that piece closed with the following:

“The city is fast growing towards Rosedale, and in a few years the chapter of his immediate work will be closed, and streets and buildings occupy the ground where the rare trees he planted and loved still interest the lovers nature.”

Having worked at Landreth’s (a prominent seedhouse at 21st and Federal streets, in what is now south Philadelphia) and Lemon Hill (which would go on to be the beginnings of Fairmount Park, but prior to that was a major horticultural site), Robert Buist, Sr. was well grounded as a plantsman.  Originally from Scotland, Buist came to the US, as did many other botanists and horticulturalists in the early days of the country, to seek opportunities that just weren’t to be found in the old world.  And he found them, and he capitalized on them, becoming one of the most well regarded horticulturalists in America, and also becoming a very wealthy man in the process.  [to read more about Robert Buist, see here]

The Sophora also traveled.  It was introduced into Europe by Pierre Nicolas D’incarville, a French missionary working in China, when in 1747 D’incarville sent seeds to France from China, and 30 years later, according to a recounting by the 19th century botanist, Jean Henri Jaume St. Hilaire, it was growing in Saint Germain, and by 1824 the Sophora was grown throughout Europe.

For some reason though, it didn’t catch on in America – in Daniel Jay Browne’s “Trees of America” in 1846, it doesn’t have an entry.  And, according to Henry Winthrop Sargent, in the 7th edition of the “Treatise on the Theory and Practice of Landscape Gardening”, Andrew Jackson Downing, in his earlier edition of that work (the 4th in 1849), classified Sophora as a shrub because it was quite rare in Downing’s time, and there were no large trees of it then, in this country.

In 1919, Samuel Baxter, at the time the arboriculturalist for the city of Philadelphia, wrote an article in the National Nurseryman on this Buist Sophora, the one on Hobson Street – he mentions that it was endangered by the construction of nearby housing, and he writes that “It is the largest in the vicinity of Philadelphia, where several fine specimens are to be found”.  And so we know that the Sophora was planted in various places in Philadelphia by the early 20th century, but it it doesn’t sound like it was abundant.

The Sophora, today, is reasonably common in Philadelphia – along Windrim outside of the Wayne Junction train station, along the 7th Street side of McCall School in Center City, and a number of other places, its bright white flowers blossom in summer, and its rich foliage greens from spring to summer, and its sturdy branches hold high through the winter.

And on Hobson Street, the largest and quite possibly oldest Sophora in the city drops its seeds all over the sidewalk.  Sitting on the pavement, those seeds won’t germinate and grow, but placed in some dirt and given a little bit of care, these descendants of a tree that has outlasted General Electric, that is there due to one of the most important nurseryman of his time, these seeds that are genetically linked back to France and from there onwards back to China, given just a small amount of tending, they can grow again, and make new trees with historic roots.

(NB: the tree pictured here might be the tree described above; The National Nurseryman, Vol. XXVII, No. 4, April 1919: “Incidentally, the tree illustrated might well have been a candidate in the recent competition of the Genetic Society to locate the largest tree of a species, for the trunk is three feet in diameter, and the spread of branches seventy feet across. It is the largest in the vicinity of Philadelphia, where several fine specimens are to be found. This particular tree may have been planted by Robert Buist, the well known horticulturist, who died in 1880 and whose place is not far from that of John Bartram, the botanist to whom we are indebted for the discovery of the rare Franklin tree – Gordonia pubescens. The writer “found” this Sophora recently on the old Buist estate where it narrowly escaped being cut down to make room for the housing of Uncle Sam’s ship builders at Hog Island on the Delaware River. Uncle Samuel’s representatives, however, were appreciative of the value of trees to a community and so the layout was adjusted and a certain area set aside for the worthy twofold purpose of providing a small park and the preservation thereon of the existing fine old trees.”)