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The Cholla Cactus Didn’t Bloom This Year — California Scientists Team Up To Find Out Why

Ryan Buck and Lluvia Flores-Renteria inspect the cholla cactus at the Desert ...

Photo by Megan Burks

Above: Ryan Buck and Lluvia Flores-Renteria inspect the cholla cactus at the Desert View Tower, Aug. 2, 2018.

The desert floor just east of San Diego was a stark contrast this spring to the showy display of flowers during 2017’s super bloom. In March, San Diego State University researcher Lluvia Flores-Renteria and her students found none of the Wolf’s cholla — a common cactus in the valley — had bloomed.

The waist-high tangles of cylindrical branches covered in fine spines typically put out vibrant red and yellow flowers. But this year, their only show of color was up at the Desert View Tower, a historic roadside attraction where the property’s owners douse them in water regularly.

“This year we’ve seen a shift, but we don’t know if it’s related to precipitation patterns or temperature or something else,” said Flores-Renteria. “So if we have historical data, then we can start asking these questions.”

That’s why Flores-Renteria and her colleagues at SDSU will join biologists across the state this fall to digitize and merge all of their plant specimens into a single database. The idea, kicked off by a researcher at Cal Poly, San Luis Obispo and funded with $1.5 million from the National Science Foundation, is to help scientists track when plants flower and fruit over time.

They have a hunch that climate change is significantly altering the reproductive cycles of plants, but right now all they have is anecdotal evidence, like this lackluster year for the cholla.

Photo by Megan Burks

Michael Simpson shows off a plant specimen in the San Diego State University Herbarium, July 31, 2018.

The digitization will take place across 19 universities, botanical gardens and natural history museums that house herbaria, or archives of dried and pressed plants. SDSU alone has more than 21,000 specimens, some dating back to the 1800s.

When digitized, scientists will be able to see high-resolution photos, tell whether the plant was flowering or blooming when collected, and compare that to other specimens of the same species to discern whether the reproductive cycle has shifted over time.

Researchers on the East Coast have found such shifts, believed to be connected to global warming. Though she can’t yet prove it, Flores-Renteria believes that’s what is affecting the cholla, too.

“If you see a large fruit that looks juicy, let me know,” she said on a recent trip to the tower to see if the chollas that did bloom produced any fruit.

They hadn’t.

“Well, we cannot really find anything. That’s sad,” Flores-Renteria said as she inspected the plants with a pair of kitchen tongs.

Even the blooms she and her students had covered with protective bags after pollinating them by hand failed to produce mature fruit.

“When we came here and did the manual pollinations, we saw the bees. The bees were very active,” Flores-Renteria said. “So the natural pollination occurred and the manual pollination occurred, but as you can see, all of the fruits are being aborted.

“So that’s really scary, actually, to see all of these plants not reproducing sexually.”

Photo by Megan Burks

Lluvia Flores-Renteria inspects a dried cholla fruit, Aug. 2, 2018.

The plant can still clone itself by dropping sections off its branches to take root elsewhere. But student Ryan Buck said the adaptation isn’t a fail-safe.

“Just imagine that you bud off and you start cloning and there’s just a whole population of you. And let’s say you’re allergic to strawberries and the only food source you have is strawberries. Every single one of you is going to die because you can’t eat,” he said. “So there’s not enough genetic diversity to keep going. Some species can evolve and adapt to that, but that’s going to take a lot of time, and at the rate that climate change is going, they don’t have that time.”

When asked why that matters, Flores-Renteria explained the cholla is a foundational species on which the desert ecosystem relies. If you pull out one thread, things begin to unravel. And she said, just look:

“It’s magnificent.”

Each night as the sun sets, its rays get tangled up in the tiny spines of the cholla, giving the plants an otherworldly glow. Yes, they’re foundational. But at the end of the day, they’re magical, too.

Flores-Renteria will continue to track the cholla to see if this year is an anomaly or a symptom of climate change. She could have enough evidence, thanks to the digitization project, to prove her hypothesis in a few years.

The Cholla Cactus Didn’t Bloom This Year — California Scientists Team Up To Find Out Why

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