These yellow flowers cover the 110 Freeway walls. How they got there

My 110 Freeway commute to LAist’s Pasadena office is lined with beige, concrete walls that (try to) insulate the surrounding neighborhoods from the din of my car and the thousands of others on the road.

But on a recent morning, a thick garland of yellow flowers spilled over the top of the sound walls from the 91 through the South Figueroa Corridor and glowed in the early light.

I wondered what could grow, let alone thrive, in such an unforgiving place. So I put my journalistic powers to use and found more questions along the way.

‘Showy, but invasive’

Since the 1940 opening of the Cahuenga Pass Freeway, Angelenos have complained about highway noise. The first soundwall was finally built along Interstate 680 in Milpitas, near San Jose, in 1968.

As of 2023, there are about 338 miles of soundwall in L.A.and Ventura Counties according to Caltrans' office of environmental engineering (including one segment made from mulch in Long Beach.)

L.A. Metro and the State Department of Transportation collaborate to build the county's soundwalls, and Caltrans is responsible for their upkeep. I sent one of their representatives a photo taken from my car window and received an answer two days later.

Dolichandra unguis-cati. Common name: “cat’s claw” vine.

Cat's claw flowers engulf the sound wall on the westside of the 110 sound wall near Vernon Avenue on April 10, 2025.

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Mariana Dale

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LAist

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The Caltrans spokesperson ended their email with “please don’t hesitate to reach out if you have any questions.”

And I did have questions.

Because when you punch cat’s claw into Google, one of the top search results is a university article that calls the “showy but invasive plant” a “major nuisance” that is illegal to sell or buy in Florida.

“Invasive plants don't support our local fluttery and flying and crawling species — birds, bees, butterflies, caterpillars,” said Erik Blank, a horticultural educator at the nonprofit Theodore Payne Foundation. “They may out-compete the plants that do support those species.”

The climbing vine is native to the West Indies, Central and South America, but is now found around the world from China to Australia. Blank pointed me to a USDA report that estimated that cat’s claw could establish itself in about 20% of the United States.

“That tells me this plant is super adaptable,” Blank said. ”I admire plants like that, but I don't wanna… play with fire, so to say.”

In mid-April 2025, I noticed thick garlands of yellow flowers spilling over the top of the sound walls from the 91 through the South Figueroa Corridor.

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Mariana Dale

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LAist

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I thought about this the next time I drove on the 110 and noticed the plant had crawled up and obscured part of a diamond-shaped highway sign, which now read “____ WORK AHEAD.”

Changing the narrative on urban plants

Alessandro Ossola studies how plants can create greener, healthier cities at the University of California, Davis. One of his current research projects examines how vines can cool urban spaces.

“The beauty of vines is that they grow fast — much faster than a tree,” Ossola said. “We can actually use the two of them together because if we want to green cities faster, the tree is your long-term goal, right? But the vines can be that stopgap measure to create shade fast.”

He was familiar with the vine because it grows in the UC Davis greenhouse and features in a lesson on “vines and climbers.” His students, like me, are fans of the yellow flowers.

“It's really, really hard to find plants that can thrive in these [urban] environments,” Ossola said. “Particularly flowering plants that can also bloom and somehow beautify landscapes that otherwise would be just gray concrete.”

The plant's eponymous "claws" are specialized leaves that help the vine climb with—intention! “They use another object in the landscape to be able to position themselves so they can maximize the amount of light that they can get,” Ossolsa said.

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Mariana Dale

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LAist

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Part of the reason the vine thrives along the 110 Freeway is that it doesn’t need much water, he said. Florida’s comparative abundance of moisture likely contributes to the plant’s invasive nature there.

Cat’s claw is not on California’s list of invasive plant species. Ossola said that Southern California’s frequent droughts and maintenance can help keep the plant in check.

“We need to change, a bit, the narrative where you plant and forget,” he said. “Plants need our care. They can provide us with a lot of benefits, beautifying our cities, providing cooling and so on, but they need a bit of care.”

Cat's claw flowers turn to string-bean like seed pods that eventually release brown seeds with "paper wings," according to the University of Florida.

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Mariana Dale

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LAist

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He said cities can benefit from a variety of plants, both native and exotic.

“The best solution will be to create a biodiverse landscape where you don't have only this particular species, but you have many different species,” Ossola said. “Even if one species fails or becomes invasive, then the rest of the ecosystem is somehow well balanced.”

Flourishing in a freeway environment

The Caltrans spokesperson forwarded my questions to the department’s regional landscape architecture team.

In a statement, the team wrote that the vine I saw was planted around 1996, “a boom time for soundwall construction.”

Around that time, I imagine it was becoming clear that while the walls are useful, aesthetically, they leave a lot to be desired.

The wide expanse of concrete is blank canvas for enterprising taggers and the walls can radiate heat into the surrounding community.

“Vines were field-tested to see which vines would flourish in a freeway environment where wind, glare, pavement temperatures, and road dust can damage a plant's health,” they wrote.

As to whether the plant could threaten the natural environment?

“Almost any plant, whether native or non-native, can be considered invasive in a pristine environment if introduced,” Caltrans wrote. “The vine in this landscaped area receives periodic maintenance, which keeps its growth in check."

It’s unclear why, but Caltrans couldn’t find records of the cat’s claw planted elsewhere in the region.

“There were a few previous locations, and due to construction, the vines were removed and never replaced in kind. To my knowledge, the cat's claw vine has not been used in over twenty years.”

I, for one, am grateful for the pop of color along my morning commute — and the reminder that a resilient environment is one that includes the contributions of many.