For generations, collard greens have formed an important part of African and African-diaspora diets around the world.

The leafy vegetable is a quintessential part of African American, Southern and "soul" foods in the United States. Collards are also important in some regions of Africa: In Kenya, where they are called sukuma wiki, they are one of the most commonly consumed vegetables.

Until now, the consensus scholarly view has held that collards came to the Americas early in the 16th century with Spanish, Portuguese or English Europeans, who introduced collards as a garden plant that was then taken up by enslaved Africans.

But our discovery of collards growing in southern Moroccan oases gardens put us on a quest to better understand the path collards took to arrive in the American South. Our new research suggests that they arrived in Morocco with early Muslim traders, adding the potential of a stop in North Africa hundreds of years before they journeyed to North America.

Moreover, the similarity in recipes from Morocco and the American South supports the idea that Moroccan oases may have been a stop in the journey collards took to America.

Collard greens belong to the species Brassica oleracea, which also includes broccoli, cauliflower, cabbage, kohlrabi and Brussels sprouts. The huge genetic diversity within the species has complicated research into where collards were first domesticated and how they moved around the world.

Evidence suggests collards were likely domesticated in the Mediterranean, from wild relatives also found on coastlines around the Mediterranean. Their path from the Mediterranean to the American South remains unclear.

As ethnobiologists and researchers interested in traditional foodways, we have been studying leafy vegetables across Morocco for 20-plus years. Yet we had never seen collards growing in any of the other areas across north and central Morocco we had worked in.

While working in date palm oases in southern Morocco, we were, therefore, surprised to find collard greens in the gardens of African diaspora communities that are descended from enslaved people brought across the Sahara.

Suspecting that the presence of collards in an important ancient trade hub might shed new light on the history of the plant and its journey to the Americas, we began collecting stories, proverbs and recipes from the African diaspora communities and searching for potential links to other places where collards are culturally important.

Tracking down information was complicated: Leafy vegetables rarely show up in the archaeological record, and historical texts use the same words to refer to heading cabbage - what most people call "cabbage" today - and nonheading cabbages such as collards and kale, which were more common than heading varieties until fairly recently.

Historical texts in English refer to both as "cabbage" or "cole." In Spanish, both are called "cole"; and "couve" is used similarly in Portuguese. Arabic texts use "kornub" to refer to both. However, this was one important clue to the ancient Arabic origins of collards in Morocco. In Moroccan Arabic, cabbage is called "mkouwer" or "melfouf," and cauliflower is usually called "chou-fleur" - a word derived from the French. Moroccans only rarely use "kurunb," from classical Arabic, to refer to cauliflower.

The communities that grow collards in Morocco call it by the ancient Arabic name "kornub."

As we searched, we were astonished to find a recipe in a 10th-century cookbook from Baghdad that was almost identical to how people in Morocco cook collards. Moreover, the cookbook describes in detail a variety of cabbage with smooth leaves called "kurunb Nabati," or "Nabatean cabbage," where only the leaves are eaten. That, and the fact that the preparation description refers clearly to leaves rather than heads, offered further evidence that this was referencing collard greens.

We pieced together a possible historical route from Baghdad to Morocco from the rare cases when historical documents included specific descriptions of the plant.

One report from a British explorer who traveled through Algeria in 1860 included notes about finding various types of "cabbage" and about a man who had stolen cabbage and had it concealed under his shirt - suggesting flat leaves rather than heads.

Moreover, a colleague at the Oman Botanic Garden told us that collards are grown in oases gardens in the Hajar mountains of Oman.

After piecing it all together, our research suggests that collards arrived in Morocco from Iraq and Oman with early Kharijite Muslim traders in the eighth century. These are the same people who founded the great city of Sijilmasa and ran the early trade routes that carried gold and enslaved humans across the Sahara.

The presence of collards in Moroccan oases also necessitates a reconsideration of the currently held assumption of how the vegetable arrived in the Americas.

We couldn't find concrete evidence of connections between Morocco and the arrival of collards in the Americas, so it's impossible to say that the consensus scholarly view on collards' journey is wrong. Still, the currently held assumption that collards arrived in the Americas with settlers and were adopted by Africans who used them as a substitute in leafy green recipes from Africa needs revisiting.

Indeed, unlike common collards recipes, most leafy vegetable recipes from West and Central Africa include fish, ground nuts or peanuts and palm oil. Compared with leafy vegetable recipes from West Africa, the collard recipes used in the United States today are strikingly similar to those from Morocco and 10th-century Baghdad. The similarity in recipes from Morocco and the American South suggests that Moroccan oases may have been a stop in the journey collards took to America.

The story of collards in the Moroccan oases is an opportunity to consider the ways the transatlantic trade systems were entangled with the trade routes and systems before them, especially the trans-Saharan trade routes, and what these entanglements mean for the foodways of Africans and African diasporas around the world.