Why are air fresheners for cars shaped like trees, even if they smell like vanilla? The answer involves pin-ups, chemistry, and a little crying over spilled milk.

In 1952, a chemist and perfumist named Julius Samann was chatting up a milkman in Watertown, New York, where Samann had settled down to explore new business opportunities. The delivery driver was complaining that his truck had been fouled with the odor of spilled, soured dairy products that no amount of cleaning would erase.

Samann, who had spent years in the Canadian wilderness extracting pine needle oils, had an idea: seal a fragrance in something absorbent like blotting or filter paper and hang it inside the vehicle to mask unwelcome scents. He drew up a United States Patent and Trademark Office application for a “container of volatile substances” and submitted it in 1954. On August 7, 1956, he was granted patent number US2757957 for this:

As you can see, that is not a tree. Samann’s original intention was to offer an air-freshening product in the shape of the pin-up models that were popular in the 1950s. The cut-out featured a woman, her back arched, with a string affixed to her head. He sent out samples to gas stations, who reported brisk sales; cab drivers appreciated how they could hide the stink of cigarette smoke and passenger body odor. Encouraged, he started the Car-Freshner [sic] Corporation in Watertown.

At some point, though, the incongruity of a pine-scented woman must have bothered him. In 1959, he filed an application for an “improvement” over his previous sketch.

The abstract Evergreen tree shape made more sense, both in context and in function. Samann’s invention called for a scented paper covered in cellophane that would trap the fragrance until the consumer was ready to use it. By slowly pulling down the plastic over the branches across a period of weeks, more of the odor could be retained for later use.

Samann called his aromatic add-ons Little Trees. In an example of iconic brand shapes, the Trees became instantly recognizable. This was both a blessing—the product has sold billions, according to Car-Freshner estimates—and a curse.

Because the Little Trees are so familiar, people often mistake it for a generic design. As a result, Car-Freshner has been very, very aggressive in protecting their trademark over the years. When Old Navy produced a t-shirt depicting a similar shape, they sued. When Rite-Way marketed a line of knock-off fresheners, they sued. When Glade issued a tree-shaped plug-in for the holidays, they sued. When Urban Outfitters released tree-shaped holiday gift tags, they got pretty upset. In many of the cases, Car-Freshner Corp. emerged victorious. (Against Glade, they had to settle for a dismissal.)

The Ttrees have also entered the legal system in another way. Several states, including Michigan, Illinois, and Virginia, have passed laws prohibiting objects hanging from a car’s rearview mirror on the grounds it could potentially obstruct a driver’s view of the road. Several cases have been brought before courts alleging that law enforcement is using the air fresheners as pretext to make traffic stops with vehicles they suspect harbor drugs. In Wisconsin, one driver who was found to have marijuana in his vehicle had his conviction reversed because the officer had pulled him over owing in part to a swinging pine tree in his cabin. The stop was considered unlawful.

It’s not likely Samann, who died in 1999, could have imagined his invention would one day be a pawn in the war on drugs. His family-owned Car-Freshner Corp. continues to manufacture Little Trees in Watertown. Recently, they’ve protested plans to build a meat-packing plant close to their factory. They claim the smell of a slaughterhouse would overwhelm their ability to conduct proper fragrance testing. Masking spilled milk is one thing; covering up animal carcasses is asking a lot.