The fruit of the liquidamber is a hard, brown, spiky ball slightly smaller than a ping-pong ball. It is strong enough to resist breaking when stepped on, and itsround shape makes it roll like a marble when a person's weight lands on it.

According to Public Works Director Marvin Rose, the liquidamber is the second most prominent tree of the 36,000 trees in the city. At 3,800, they number just behind the magnolia tree. Each tree produces thousands of the hard, spiky balls, and when they fall, they cover sidewalks, lawns and driveways.

Werner Gans, 73 and a resident of Sunnyvale for 46 years, has a number of the trees in his neighborhood, one just a few houses from his home on Lanark Court. He used to walk around his neighborhood on a regular basis but has reduced his walking sojourns because of the liquidamber fruit. Gans said he has fallen almost a dozen times over the years because of the prickly balls, and his wife has fallen as well.

"It's a problem and the city needs to do something about it because it's a safety hazard," Gans said. He was standing under a liquidamber tree that is devoid of leaves but still has scores of balls hanging from it.

Rose said the city has gotten a number of complaints over the years but because of the sheer number of trees and the state of the city's budget, there is little it can do about the problem right now.

He said that in the past if residents complained, the city brought a high-powered hose out to blast individual trees with water and knock the balls off. He said that significantly reduced the amount of prickly balls on the ground. But that method was stopped because of budget cuts.

There is a chemical that can be sprayed on all types of trees to cut down on their fruiting, but it's even pricier than the water blasting. And the city tries to avoid using chemicals unless absolutely necessary.

Rose also stressed that the liquidamber is a very popular tree in Sunnyvale--something Gans also said--because it's one of the few trees in the area that undergo a dramatic change of color when the seasons change.

"It's a beautiful tree; the leaves turn a reddish color in the fall," said Gans. "It's beautiful, other than the fact that it drops these balls."

Rose said the city is ready to address the issue and will be looking at it as a study item in August. There are a number of things the council can do about the problem at that point.

One possibility is changing the designation of a "hazard" for trees in Sunnyvale. Rose said a tree can only be removed right now if it is diseased or presents a safety hazard, as it would if the whole tree or a branch fell. But the fruit of a tree does not currently fall into the category of potential hazard, something Gans disagrees with.

"If there were just a nuisance, I wouldn't be concerned, but it's a safety hazard," he said. "I talked to people who were riding their bikes and they said, 'Man, if you think it's bad when you're walking, you should try hitting one on a bicycle."

This is not the first time liquidambers have presented a problem for Sunnyvale. The city has stopped replacing old or damaged liquidambers because they were already causing damage. The roots of the liquidamber spread over a wide area quickly and damage sidewalk and driveway cement easily.

The city also stopped replacing them because more than 10 percent of the trees in Sunnyvale are liquidambers, and Rose said they want more variety because that prevents diseases--which can sometimes affect only one type of tree--from wiping out a large chunk of Sunnyvale's flora.