A botanist at the Brooklyn Botanic Garden, Steven Clemants, took the The New York Sun’s Hana Alberts on a walking tour of Lower Manhattan’s flora. Using binoculars, he talked about how European weeds and “urbanophile” plants can infiltrate the gravel at ground zero, why moss can grow in the shadow of Trinity Church, and why it’s important to get more greenery back on city streets.

Q. What is growing in ground zero now?

A. The plants of the cottonwood tree, wild lettuce. They are pretty typical species. There’s a mullen, there’s a dandelion, there’s a mugwort, which is a real common plant. You can find it growing out of the side of buildings. The brick is decaying, seed can get in, and it will grow out. It’s a very tenacious weed from Europe, very aromatic, so it was probably used as a medicinal plant at one time. But in the same genus is the plant that they get absinthe from. You know what absinthe is? And that actually grows around the city, too.

So they are not weeds?

Well, they are weeds. “Weed” is a very generic term that is not usually used. These are ruderal plants – these are plants that grow out of rubble. In Europe there was a marked increase in these ruderal plants – some of which are rare – probably in World War II, because of all the bombings and all the rubble heaps. Most cities try not to have that, so you don’t have that problem.

Are their roots actually in the gravel?

There are very few things that are ever going to grow without having some sort of rooting substance, usually soil of some sort. Most likely, this stuff was gravel that was brought in for construction purposes, so it’s seed that’s in gravel from the site that it came from. But in Scandinavia, for instance, they dug up old foundations and found seed underneath the foundation that was still viable. And these were buildings many hundreds of years old. So the seedbed can survive for a long time in certain species, too. But I doubt that in this site this would be the case.

Then where do the plants come from?

Most of these are from Europe and were brought in for a purpose, though some of these might have been brought in as stowaways. The ships that came over with passengers needed ballast in the bottom to keep it upright, and they used to use cobblestones. Then they’d pave the city with the cobblestones. That’s one way that seeds got in.

They could also get in by raw wool. There used to be a wool factory in Yonkers that imported raw wool from all over the place. And around 1900, a botanist went out and looked in the waste piles and found all these plants coming out that no one had ever seen before or since, from Argentina and Australia and things like that. And they were just part of the wool.

How can plants like this flourish in New York City?

One thing that people have started to hypothesize is that some of these species evolved with the growth of cities. They are urbanophiles. We’ve had cities for 2,000 or 3,000 years now, especially in the Mediterranean, and most of these come from the Mediterranean. That probably is enough time for some of these things to evolve.

What causes this urban heat island is that we release so much heat in the winter, buildings are poorly insulated, steam pipes are in the ground. The temperature in the city is going to be 10 degrees warmer than the surrounding area. So we get kudzu that grows in the city in spots. That’s the plant that grows in Tennessee that gobbles up houses and stuff. It’s a big vine, but it wouldn’t normally grow this far north because it flowers very late in the year. Fruit would normally be killed off by frost this far north, but we don’t get frost that early, so it is able to survive here.

How do you feel about vegetation on the World Trade Center site?

What’s nice for me, although I have my own feelings about what this site should be, is that, if left by itself, nature will come back and take it back, much like what happened in “Planet of the Apes.” Nature can heal its own wounds pretty well.

There was virtually no vegetation on the site when it was functioning. The plaza had maybe a few tree pits. There really wasn’t anything else. A few planters along the sides of the street to keep the cars from getting in. But it’s a different look right now.

So what was this site specifically here, historically, if we wanted to restore it to what it was? This was probably mudflats. The edge of the island was close to Church Street. It was very early landfill. You really can’t restore it fully. You couldn’t restore mud flats without a lot of work. You know, it would be an interesting proposition.

I don’t know what the Lower Manhattan Development Corporation would say about that.

I had this idea for Governor’s Island, the southern half of it, which is all these dorms. I just think they ought to tear them down and bring back the mudflat that was there. If they can’t come up with any other idea, just keep the historic part and put up a mudflat. These flats are really valuable for birds. Herons need little islands. We just tend to destroy those sorts of habitats because it doesn’t have functions that we find acceptable or useful.

What is special about Trinity Church?

Graveyards, not in cities so much, but elsewhere, are really useful areas to look for interesting plants. In the prairies, that’s where you often find prairie plants preserved, because they never plow the graveyards.

This is oxalis, it’s a plant that grows in sidewalks quite often. The fruit it explosive – it bursts open. This is plantain. It used to be called white man’s footprint. The leaves look vaguely like a footprint, but the Native Americans used to call it that because everywhere the white man went, this plant was found. It was probably introduced as a laxative.

Very few mosses grow in the city now. You can see the moss here, and there’s actually a liverwort a little further down. They need moisture. Urban areas are very dry often, because we let the water run off. Mosses and liverworts and ferns, for that matter, need to have water for the sperm to swim to the egg, to fertilize. So you don’t see them too often, especially this luxurious a growth, in the city.

What is your botanic wish for New York City?

One of the things I want to do, and I think others want to do, is try to bring more nature back into the city. To start to get people to recognize that there is stuff like this, pockets that are interesting. Also, you can do a lot more, just with the regular streetscape. I was in Chicago a week and a half ago, and the mayor gave a talk at this conference. He is dedicated to doing everything he can to try to bring back vegetation to Chicago, putting in thousands and thousands more street trees. And I think that’s phenomenal. It can really benefit the city. There was a study presented at this conference, looking at crime in buildings in relation to whether they had any trees outside. And those buildings that had five trees outside had significantly lower crime rates than those buildings that had no trees outside. There’s no reason why we couldn’t put more planters with flowers out.

STEVEN CLEMANTS
Native of suburbs of Minneapolis

* Resides in Park Slope

* Coordinator of the New York Metropolitan Flora Project

* Serves on the New York State Invasive Species Task Force, the Invasive Plant Council of New York State, the New York City Soil and Water Conservation District Technical Advisory Board, the Nature Network steering committee, and the New York Urban Biosphere Group

* New York Natural Heritage Program Botanist from 1985 to 1989, where he developed the botanical component of the Natural Heritage Database, surveyed New York for rare plants, worked with the U.S. Fish and Wildlife Service to recover plans and status reports of federally endangered and threatened species, and worked with the New York State Department of Environmental Conservation to write the state’s endangered and threatened species regulations

* Earned a Ph.D. in biology from the City University of New York, a Master of Science in botany and horticulture from the University of Minnesota, and a Bachelor of Science in botany from the University of Minnesota