City of Seeds

With an influx of people from all over the world, the city can become a hothouse for foreign flora.​

By Daniel Mason

Painting of two statues in a grove of trees.

Entrance to the Giardino del Lago, Villa Borghese, Rome, by Gustav Wilhelm Palm, 1844. © The Metropolitan Museum of Art, Thaw Collection, jointly owned by the Metropolitan Museum of Art and the Morgan Library & Museum, gift of Eugene V. Thaw, 2009.

Early last summer I found myself in negotiation with my landlady over the loquat tree outside our bedroom window. According to our neighbor, the tree, which rises from a six-inch gap between the wall and the driveway, was imperiling cars with its fruit and power lines with its branches. My landlady wanted to cut it down. I didn’t. The tree wraps the entire northwest corner of the apartment in a dark green canopy, transforming the bedroom into a kind of glassed-in treehouse from which we can look in upon bird’s-nests and conferences of squirrels with the kind of intimacy reserved for a nature documentary. In the late spring, we can reach out and pick its fruit.

Of course, my neighbor’s contention was understandable. No one had planted the loquat. It was an escapee from another garden, strictly speaking a “weed,” and a big one at that. Left unchecked, its roots would buckle the driveway, its limbs burst the windows. Already, in high winds, the branches screeched menacingly across the glass. In the dusty cracks between the concrete, seedlings would germinate, grow.

Whether or not my neighbor had such dramatic images in mind, I don’t know. But the struggle between city and nature is an old conceit. One has but to look to the oaks growing on Caspar David Friedrich’s ruined monasteries or the grass that “o’erspreads” the fallen city of Browning’s “Love Among the Ruins” to see how plants have classically been understood as the definition of the city’s demise. When the great fifth-century Chinese poet Bao Zhao wrote with grief of the fallen city of Guangling, he titled his famous Fu, or rhapsody, the “Wu-cheng,” words often translated in anthologies as “ruined city” but which literally means one that is “overgrown.”

A View of the Upper Parts of the Ruins of the Baths of Diocletian, by Giovanni Battista Piranesi, 1774.

A View of the Upper Parts of the Ruins of the Baths of Diocletian, by Giovanni Battista Piranesi, 1774. 

“Wet moss clings to the wells / Wild vines entangle the path.” Indeed, looking out from our window, past the tree, it was not hard to see a similar process at work. There were clovers in the driveway and a deodar seedling sprouting on the asphalt rooftop of the carport. There was a tree-of-heaven emerging from the lightless depths beneath another neighbor’s house. And yellow bursts of mustard on the sidewalk, and tangles of pink filaree, and purple cheeseweed. And dandelions. Dandelions, everywhere.

Yet this wasn’t the simple fact of nature’s return. There are no loquats in the native woods a mile away; they are indigenous to southeastern China. There is no deodar cedar (from Kashmir), no tree-of-heaven (from northeastern China and Taiwan), no native cheeseweed or filaree. What was blooming outside was not some sort of natural reclamation. But neither was it the deliberate work of man. It was something different, unique to the city, bound to its inhabitants and, the more I realized, inextricably tied to its fate.


Fourteen hundred years after Bao Zhao’s eulogy for Guangling, the English physician Richard Deakin looked out upon the ruins of another city and also found flowers. But what for the Chinese poet had been a source of grief, for Deakin was a moment of misty nostalgia. Such plants, he wrote, “form a link in the memory and teach us hopeful and soothing lessons amid the sadness of bygone ages.” He even berated the city restorers for destroying the “solitary lesson which so magnificent a ruin is calculated to make upon the mind.”

The occasion for Deakin’s meditations was the 1855 publication of his Flora of the Coliseum of Rome. In cataloguing the “most graceful and lovely objects”—420 species of them—found upon the ruins, the author of British Ferns and Their Allies was joining a tradition of urban botany then two-and-a-half centuries old. Wall rue, sea lavender, and pellitory of the wall had been mentioned in John Gerard’s 1597 Herball as growing in the “corners of church buildings” and “among rubbish and other stony places.” Surveys of urban plants had been published for London in 1632 and Paris in 1635. In the 1668 Flora of England, John Ray, the great English naturalist, noted Sisymbrium, then called wild mustard of Naples, growing on the remains of London’s St. Paul’s Cathedral, two years after the city burned in the Great Fire. At least two other botanists had been to the Colosseum before Deakin stared up at its walls. There were rubble floras of Palestine and Algiers, and soon to be one of the Palais d’Orsay, destroyed during the Paris Commune of 1871.

There is a city in which you find everything you desire—handsome people, pleasures, ornaments of every kind—all that the natural person craves. However, you cannot find a single wise person there.

—Rumi, 1250

Like most of these works, Deakin’s Flora addressed the medicinal qualities of the plants he found: many early botanists were physicians seeking to expand their pharmacopoeias. And yet, by looking for plants in debris, Deakin, like Gerard and Ray, seemed to recognize the central, strange observation that lies beneath the contemporary study of urban botany: the flora of the city is essentially a flora of the city’s destruction. Unlike the managed green of parks and gardens, which only grow in pockets of protected isolation, the wild plants of the city—known as ruderal, after the Latin rudus for ruins or rubble—need the cracks: the pavement split, the palace abandoned. The fabric of the city as well as the fabric’s tear. Most, like my loquat, have failed to become established in nearby forests; they thrive only where the land has been violently disturbed.

It is not surprising, then, that the great modern advances in the study of the flora of the city were made in cities destroyed during World War II, nor that its center of study was Germany. While Ray found Naples mustard on the burnt remains of St. Paul’s, in Berlin it was another invader, Jerusalem oak goosefoot, that found the bombed environment of that city so favorable as to be ubiquitous within a year. The goosefoot was later accompanied by others, like the tree-of-heaven—the Asian native that also grew in Brooklyn—and the giant goldenrod, so American as to be the state flower of both Kentucky and Nebraska.

In the spaces opened up by the bombing, German botanists found a new science, a “tremendous natural experiment,” in the words of one observer, “which with respect to its size, must be compared to the populating of new habitats created by volcanic activity.” Urban planners spoke of “New Life from Ruins,” a “green veil,” a cure for the “psychosis of rubble of narrow-minded people.” Green space was seen as a way to separate from the past, a fresh start, although, somewhat ironically, such programs—the clearing of tenements, the creation of organic urbanism—had themselves been part of the Nazi city order. Indeed, even the language of postwar urban planning remained haunted by the very ideology it was trying to transcend. The German word for “new habitats” cited above is Lebensraum.

Just as German botanists spread over the rubble mountains of their cities, in England, too, war afforded observations previously impossible. In his April 24, 1943, Nature paper “The Flora of Bombed Areas” Professor Edward Salisbury of Kew Gardens found in the bomb sites perfect laboratories for the study of plant dispersal. But unlike the German proclamations of rebirth, Salisbury had little time for such indulgences. Perhaps it was because the war wasn’t yet over. Or perhaps he found the metaphor obvious enough. Instead, Salisbury’s paper was, emphatically, about how plants spread: elder bush by bird droppings, common groundsel on pedestrian’s boots, oats and wheat and clover in the feed bags of horses. In other cases, they were already there, waiting for the opportunity to bloom. Salisbury attributed the commonness of tomato plants directly to man’s actions, the seeds perhaps having fallen out of a grocer’s cart or a worker’s lunch, now liberated by the absence of the pavement that previously prevented their growth.

But it was wind dispersal to which Salisbury devoted his most loving attention. Fascinated by the mechanisms of seed flight, he described in detail the “silky parachute” of coltsfoot seed and the seventy long hairs of the rosebay willowherb, which open out in dry air but close when the air is moist to form “a beautiful and most efficient dispersal by air currents…brought into action under conditions most favorable to the carriage of the seeds.”

And such carriage! With other botanists he spread paper beneath each plant and counted:

Rosebay willowherb: 80,000 seeds
Common groundsel: 1,100 seeds
Oxford ragwort: 15,000–20,000 seeds
Sticky groundsel: 6,000–86,000 seeds
Coltsfoot: 6,000–9,000 seeds
Canadian fleabane: 120,000–233,000 seeds

It is hard not to see in these numbers some inversion of the casualty lists, a promise of extraordinary fecundity. The image of plant seeds rising in the convection currents that formed over the bare, hot stretches of rubble…drifting slowly…falling slowly—the willowherb, Salisbury calculated, takes over a minute to fall twenty feet—all conjure the air above London as filled with a virtual flora, colonizing the airspace through which two years before the Luftwaffe flew.

The Ideal City, attributed to Fra Carnevale, c. 1482. Walters Art Museum, Baltimore.

The Ideal City, attributed to Fra Carnevale, c. 1482. Walters Art Museum, Baltimore. 

This is but my reading. Salisbury’s single swerve from objectivity is the word “beautiful,” and it is quickly followed by more figures. But the appeal of Salisbury’s paper cannot be explained by its science alone. The Times of London sent a reporter to one of his lectures; the story ran at the top of the second page. And at the end of the war, R.S.R. Fitter, in his best-selling London’s Natural History, drew upon Salisbury’s work, invoking nature’s special compensations: the horse chestnut that rebloomed after being stripped by a bomb blast, the thrushes that sang through the raids.

I still feel comfort reading of this expression of resilience, and the popularity of the Natural History suggests that postwar Londoners felt something of the same. And yet, paradoxically, for the city to be reborn, the plants that heralded this regeneration would have to be destroyed. Within a few years, the London grounds upon which the willowherb appeared would be paved over. In Berlin, a few civic movements to preserve wild green spaces created by the bombing eventually capitulated to park or building developers. And even in those corners of the ruined cities that remained untouched for years, these first hopeful species would soon be replaced by other, larger, sturdier forms.

Or perhaps there is no paradox. Such replacement—“succession,” to use the botanical term—is as old as our first myths. Man does not emerge from nothingness; we need a greener stage. Between Adam and the void, there is a garden.


It is through studies like Salisbury’s that our understanding of the city as an ecosystem has been elucidated. Cities are hotter, more overcast, and drier than the surrounding countryside. There is more particulate matter in the air and less sunlight. Trees are stunted, and those in cities where the once dirty air has been cleaned often exhibit an “urban” silhouette: a diminished trunk with thick leading branches, which shot out once the air was clean.

There is less wind generally, but it is often more severe locally, with wind tunneling, and strange sheering forces and violent eddies. There is a similarity between North American prairies and certain patches of urban wasteland, both characterized by soil disturbance by burrowing mammals—prairie dogs, us—and strong gusts of wind.

In Washington, the first thing people tell you is what their job is. In Los Angeles you learn their star sign. In Houston you’re told how rich they are. And in New York they tell you what their rent is.

—Simon Hoggart, 1990

The soil of the city, though highly variable, is in general compact (from foot traffic and heavy vehicle vibration), alkaline (because of calcium leeched from mortar and cement), and nutrient poor (with hotspots of rich organic waste). Like the air, it is polluted, a factor which affects the flora both directly, as well as through pollution’s effect on symbiotic organisms—for example, by killing insects on which the plant relies for pollination. Extreme chemical variation leads to particularly “urban” niches: heavy application of de-icing salt has prompted the inland march of species of alkaligrass and saltbush, typically found by the sea. The bases of certain neighborhood trees bear a distinct “canine zone” of velvety Prasiola algae and nitrogen-loving mosses.

With constant influx of people and material from all over the world, the city exists under constant inoculation-pressure from foreign species, like Ray’s mustard of Naples and the Jerusalem goosefoot of Berlin. Such flora betrays human behavior intimately: we eat tomato sandwiches, set out birdseed, grow wildflowers from foreign climes. We wear wool sweaters: many nineteenth-century botanical invaders of England came burrowed in wool scrap, a particularly effective form of transportation, as anyone who has worn socks through a grass field knows.

The result is a flora that is species rich. There may be fewer total plants in the city, but there are many more kinds. Niches abound: Deakin found cliff-loving Sedum in the nooks of the Colosseum walls. There is even evidence that the particular demands of a city can drive the evolution of new species (though the boundaries between plant “species” versus “varieties” is often opaque). Certain taxa of dandelion are found only on man-made sites, suggesting that they have evolved over a few hundred years to fit the particular requirements of the city. The London Plane has proved to be so well adapted to urban demands—it is tolerant of pollution, root compaction, and pruning saws—that it is found throughout the world’s cities. And only throughout the world’s cities. Most likely a hybrid of American and Oriental sycamores, it has no native habitat but the street.

The classic ecological conception of succession holds that disturbed land passes through several stages: it is cleared, plants enter, grow, compete, and replace each other, until at last the flora stabilizes. But for the most part, urban flora doesn’t stabilize. Plants enter and grow, but there is rarely a chance to progress beyond this: they are weeded, or paved over, or bombed, and the process begins again. In many ways it reflects the very dynamism of the human city, the constant influx, renewal, and decline, the resilience of the whole despite the death of the parts. In the 1935 study in which he coined the word “ecosystem,” A.G. Tansley refers to Lucretius, whose cosmology of streaming, swerving atoms presents a world always in flux:

Nor need you wonder, while the seeds are all
In constant motion, that the universe
Seems still at rest

As Edward Salisbury wrote, “Some of the seeds, like the spores of the ferns, are so small as to behave like dust particles.” It is almost as if he were channeling Lucretius, too.


In John Hersey’s New Yorker report “Hiroshima,” Miss Toshiko Sasaki, a personnel clerk at the East Asia Tin Works, having spent nearly a month in the hospital, returned to her city for the first time in almost a month. The destruction shocked her, but what particularly “gave her the creeps” was how, “Over everything…was a blanket of fresh, vivid, lush, optimistic green; the verdancy rose even from the foundations of ruined houses. Weeds already hid the ashes, and wild flowers were in bloom among the city’s bones…Especially in a circle at the center, sickle senna grew in extraordinary regeneration, not only standing among the charred remnants of the same plant but pushing up in new places, among bricks and through cracks in the asphalt. It actually seemed as if a load of sickle-senna seed had been dropped along with the bomb.”

In October of 1945, scarcely two months after the bombing of Hiroshima, the Biological Science Division of the Special Committee for Atomic Bomb Casualty Investigation and Research conducted the first of several surveys of the effects of the bomb on plant and animal life. The Science Council’s report echoed that of Toshiko Sasaki. Stimulated in part by a typhoon that struck the city on September 17, the ashen landscape was covered with pumpkin and morning glory, radish, mustard, fleabane, purslane. Like Ray’s mustard of Naples, their names betrayed their foreign origin: Erigeron canadensis, Veronica persica, Phytolacca americana. New tree growth was seen everywhere. Many trees, burned on one side, continued to grow on the other, and even those trees that seemed to have been completely incinerated began to put out buds from charred trunks and underground roots and stalks. Today over a hundred such trees remain, the most numerous of which are camphor trees, while the closest to the hypocenter was a weeping willow, only 370 meters away. I have read that you can ask any child about such a tree, and they will point the way.

Walled city, detail from the fresco Journey of the Magi, by Benozzo Gozzoli, c. 1460. © Palazzo Medici-Riccardi, Florence, Italy, The Bridgeman Art Library International.

Reading Toshiko Sasaki’s account, it is not hard to see the return of such flora as a miracle, beautiful but, like any miracle, also terrifyingly strange. It suggests the parallel existence of a hidden world, fully formed, simply awaiting the opportunity for expression. If the garden is essential to our conception of human life, it is the seed in which the garden is hidden. “The Lord God made the earth and the heavens,” reads the King James Bible, “and every plant of the field before it was in the earth, and every herb before it grew.” It is as if the seed were the first void, that impossible suggestion that something can appear from nothing. When Edward Salisbury wrote of the eighty thousand willowherb seeds, he likely knew that most would not germinate straight away. Rather, they would lodge in microscopic nooks and crannies, some to be eaten or crushed, others to be paved over, but most, simply, to wait. A square meter of urban soil can contain tens of thousands of seeds persisting in a state of suspended animation, waiting to be woken from their slumber. After the fire brigades rescued the London Natural History Museum from German incendiaries, Albizia silk-tree seeds bloomed on their herbarium sheets, liberated from two hundred years of dormancy by the precise combination of flame and water.

All of which suggests, I think, another category of urban flora, beyond the managed gardens and the wild invaders of our roads. It is a hidden, potential flora, an idea of a forest, not in competition with the city but existing alongside it, patiently, waiting to become manifest. And yet, as the fates of Hiroshima, London, and Berlin show, this invisible forest is very much real. We usually envision the seed as but a transition between two plants, but it is also possible to conceive of the plant as but a transition between two seeds. Or the city as a transition between two forests, rubble giving birth to wild vines and loquats and pellitory of the wall.

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