"It's pretty disgusting," said Jan Schneider, an office manager in downtown Iowa City whose business has a ginkgo out front.
Iowa City was one of many communities that planted ginkgoes in the 1970s only to discover that after years without problems, some of the trees can begin dropping large seed shells, creating a sticky, slimy, smelly mess. The smell makes some think of rotten eggs, while others are reminded of vomit.
Some cities have started cutting down ginkgoes, while others are standing by their trees and even planting more of them. In Iowa City, deciding to cut down another one of its few remaining ginkgoes was a no-brainer.
"We have no recourse at this point," said Terry Robinson, superintendent of the city's forestry division. "It creates a sanitation problem for us because we have to be down there cleaning it up as often as possible.
"No matter what we do, two seconds after we leave, there are more on the ground and somebody can step in it."
Officials reached a similar conclusion in Easton, Pa., where ginkgo trees were removed last year after complaints about seed shells raining on cars and pedestrians.
Easton planning director Becky Bradley said the slippery pulp was dangerous for passers-by. And of course, there was the smell.
"Stinky. I know, that's highly sophisticated, but I don't know how else to phrase it," Bradley said. "It's not a very friendly odor."
Ginkgo's defenders point out that not all the trees cause problems and the species has a lot going for it.
The tree, native to Asia, is incredibly resilient, with several surviving an atomic bomb blast in Hiroshima. Ginkgoes also stand up well to smog, road salt and pests.
But unlike most tree species common in the U.S., the ginkgo is dioecious, meaning trees are male or female. Female ginkgoes produce the troublesome seeds, which are covered in a fleshy coating that contains butyric acid, also found in rancid butter.
That has prompted cities such as Bloomington, Minn., and Lexington, Ky., to ban female ginkgoes. And Easton left the male trees while removing the females.
The problem, though, is occasionally male trees undergo a metamorphosis and begin dropping smelly seeds. That's what Robinson suspects happened to an Iowa City tree after decades without problems.
A study in Virginia found that such changes are rare, happening in about one in 100 male trees.
With that in mind, some cities are planting ginkgo trees, including Boston, Lansing, Mich., Santa Monica, Calif., and Washington, D.C.
In Washington, the city's Urban Forestry Administration allows property owners on each block to decide whether they want female trees replaced by males.
"Most people are very happy with them," said John Thomas, associate director of the forestry agency. "Some people say they moved into a neighborhood specifically because of the female ginkgoes."
Santa Monica has planted between 250 and 300 ginkgoes citywide since 2003, urban forester Walt Warriner said. He makes sure only males are planted and has returned six trees to the nursery that were sold as male but revealed to be female.
Robinson, the Iowa City superintendent, laughed when told of cities planting ginkgoes.
"I'd proceed with caution," he said.
To some, however, city officials are missing the point. What, they ask, is wrong with a smelly tree?
All the Iowa City ginkgoes were planted near the University of Iowa campus. At other universities where they've been planted, students don't seem bothered.
At Reed College in Portland, spokesman Kevin Myers acknowledged periodic reports that "something died over here" in the area of a female ginkgo tree. But there's been no thought of cutting it down.
"It's a fact of life," Myers said. "But we're happy with it. The leaves are really beautiful."
It's the same at the University of Wisconsin-Madison, where botanist Laura Jull said people notice but don't dwell on the smell of the campus ginkgoes.
Still, she enjoys watching new arrivals amble by the trees.
"I find it kind of comical watching people pass by and they're looking around like, 'Who smells?' " Jull said. "That's a little plant humor."