A Living Geographic Puzzle

At the UC Botanical Garden, Cat Callaway is piecing together crops of the world with their wild relatives. 

October 20, 2022
By Sarah Siegel, BFI Communications Assistant

Cat Callaway is no stranger to the odd job. She’s taught people how to fix bikes, worked as a landscaper, managed an organic farm, taught English, worked for a green roof non-profit, and even parked other people’s bikes at a train station for a living. But for the past eight months, Cat can be found on the hillside above Strawberry Creek, managing the Crops of the World section of the UC Botanical Garden — essentially, solving a green and living geographic puzzle. 

The section features food and other economically important plants from around the world, arranged geographically by their place of wild origin. The six main beds — Africa, Asia, Europe, Mexico/Central America, North America, and South America — feature plants labeled at the country-level. Here, crops from around the world exist in a single ecosystem, separated only by a few feet of pavement and their geographic placards. In the short time it takes for her to explain how she landed the gig, we can walk “around the world” several times.

“I think it’s fun. My idea of fun is maybe not always perfectly mapped onto other people’s ideas of fun,” Cat says of her job.

The job requires knowledge of plant genetics, anthropology, history, and the ability to keep up with the latest botanical research. Often, Cat finds continent-sized discrepancies between where crops were cultivated and where they originated from.

Growing in the Europe bed, for example, is Brassica oleracea, a plant species that has been cultivated into many familiar crops — broccoli, cauliflower, kale, cabbage, Brussels sprouts, and collard greens to name a few. It originated as a mustard-like plant in present-day Great Britain, France, and Spain, but it somehow made its way to the Fertile Crescent area of Southwest Asia where it was domesticated into the myriad of vegetables we would recognize today. It was brought back to Europe through trade, and now brassicas dominate the world, bearing little resemblance to their mustard-like ancestor despite being the exact same species.

“With broccoli, cauliflower, kale, cabbage, brussel sprouts, Chinese broccoli — all of these are the same species. If you lay out the genetics, they don’t perfectly fit genetically or evolutionarily into those categories,” Cat says. “The observable traits for us aren’t necessarily reflective of the plant’s actual genetic status.”

This is one problem of botanical geography. When the story of a crop is spread out across such a large geographic scale, it can be hard to pin down its exact origins, and plant genetics often produce more questions than answers. 

“Geography is hard. What do you call a place?” Cat says. “Africa is an entire continent, containing lots of different places. If we look at okra, for example, I am going to doubt that it’s native to the entire continent top to bottom.” 

In the Africa bed, a horned melon plant sprawls across the center of the plot, in the early stages of producing its notoriously spiky fruit. In the Kalahari Desert, the horned melon is one of the few sources of water in the height of the dry season, drawing moisture from deep in the ground and storing it within a sweet, gelatinous fruit. Growing alongside the melon is a malabar spinach and a robust African basil, known for its cinnamon flavor.

“Upon reading more recent science it looks like malabar spinach was actually native to Asia and traveled to Africa in prehistoric times, so oops, wrong bed,” Cat says with a laugh. Malabar spinach is only one example — the deeper Cat digs into the native plants of Africa, the more their stories seem intertwined with cultivated crops in Asia.

Near a failing okra plant, yard long beans and cowpeas grow side by side. Most people are familiar with yard long beans, which are commonly available in Asian grocery stores. Fewer people have heard of cowpeas, a smaller variation usually eaten as a dry bean. Cowpeas were originally domesticated in Africa, but brought over to Asia where they metamorphosed into something nearly unrecognizable — the yard long bean. Yard long beans and cowpeas are technically the same species, but you can see a huge difference in pod length and shape. 

“It’s all about selection for human taste. In Asia, people thought, ‘I really like this bean, but what if it were two feet longer? Let’s just select for that until it gets there,’” Cat says.

Knowing the rich histories of these cultivated crops, and following their path across time and space, a simple country of origin label no longer seems to tell the full story.

But piecing together the geographic puzzle — determining where native relatives of cultivated plants can be found in the wild — carries more significance than just making sure that crops are planted in the right bed. Locating the wild cousins of cultivated crops might provide the missing pieces of genetic diversity that can stabilize our farms and food systems as the climate changes.

“The wild populations of these plants are really important, because crop genetic diversity is really limited,” Cat says. “Domestication puts a bottleneck on diversity and as climate change happens, we’ve started to worry if we have enough traits available in our genetic pool to be able to keep growing the plants we like to eat while the whole global climate is shifting.”

This is a research hotspot. Plant scientists are beginning to hybridize crops with their nearest wild relatives in an attempt to re-introduce critical genetic diversity. But this practice is not new: Indigenous farmers have already been encouraging the growth of wild varieties along the borders of their farms, realizing that cross-fertilization might breed hardy and robust cultivated crops. It is easy to see how climate resilience goes hand in hand with redressing Indigenous food sovereignty and decolonizing botany.

While Cat gets settled into her relatively new role at the Botanical Garden, she is looking towards the future of the Crops of the World garden. In the coming seasons, she plans to grow wild relatives next to their cultivated cousins to demonstrate how cultivation changes a crop, selecting for its desirable characteristics and shedding its genetic diversity in the process. It’s a project that could bring the geographic puzzle into focus, but wild seeds are hard to come by.

As it is now, the Crops of the World section features plants that operate on very tight timelines. By October, some of them have already withered away for the season, while others are just starting to fruit. One of the tallest plants grows in the Central America bed: teosinte. A wild relative of corn, the teosinte is one of the only non-cultivated crops in the entire section.

“I seeded it the same time I seeded my corn, and it’s not even starting to produce female flowers yet. It’s only got the tassels on the top. And meanwhile, all the corn has come and gone. That’s one of the traits that people select for: how quickly can I go from planting a seed to eating something,” Cat says.

The teosinte stands tall and stubborn — “corn gone too far” as Cat describes it. It’s surrounded by its relatives separated by hundreds or thousands of years of harvests. 

But the teosinte seems to grow on nobody’s time but its own.