The Mystery of a Spaghetti Cactus' Journey - How did Rhipsalis baccifera cross the ocean?
This epiphyte usually grows on forks of tree branches, sometimes in the thin layer of soil in vertical rock cracks. The hanging cactus is especially common on the rough bark of the Lembobo Wattle and it is the only cactus that is indigenous to South Africa where it occurs along the coast of Maputaland to the eastern Cape and slightly inland.
Plants form pendolous clumps of thin spaghetti-like stems which hang down from the canopy like monstrous green dreadlocks. They carry tiny, widely dispersed clusters of harmless hair-like spines. Flowers are small, creamy white and rather insignificant. They are eventually replaced by small white translucent berries.
There’s one very special thing about
R. baccifera: it’s the only species of cactus that is found naturally outside of the Americas. With the exception of this weird plant, cacti occur naturally from just south of the Arctic Circle in Canada to the tip of Patagonia in South America. Thanks to their legendary survival strategies, cacti can do well it in a broad variety of altitudes and climates, from bone-dry valleys to dripping rainforests.
Unlike all of its relatives,
R. baccifera has grown wild in Africa and India at least since botanical record-keeping began. This plant has traveled thousands of miles away from all of its brethren. And despite decades of study, scientists still aren’t quite sure how it pulled this off.
R. baccifera can be found growing wild from mid-Argentina through Central America and up into the heart of Florida. But it’s also endemic in tropical Africa, Madagascar, and Sri Lanka. How did it end up all those places?
Experts have come up with a number of competing theories, some more likely than others, but all somewhat improbable.
In the first scenario, this cactus followed the path of many other plants: its seeds got a lift from hungry, migrating birds. The prevailing theory among many biogeographers is that, at some point in the past, a long-flying species of bird, snacked on berries, and then migrated to southern Africa, where they passed the seeds and begat a new plant. From there, more birds spread the cactus to more places, until it had the broad, unusual range we see today.
There are some issues with this theory. For one, frugivorous birds are not able to cross the Atlantic Ocean from South America to Southern Africa. Perhaps a tropical storm or ocean currents might have pushed the seeds from shore to shore on their own, but that’s also a rather long shot.
This brings us to the second possibility: the continental breakup theory, first advanced by botanical detectives in the early 20th century. In this scenario, neither
R. baccifera nor birds had to travel thousands of miles. The Earth did it for them.
This explanation make sense if we simply assume that our heroic cactus was around during the breakup of the supercontinent of Gondwana, about 184 million years ago. In this scenario, as Gondwana separates into what we now know as Africa and South America, some
R. baccifera is left on each side of the divide, slowly drifting apart until - millions of years of tectonic shifts later - they’re in completely different continents.
This theory has also some weak points: while no one is certain when cacti evolved, most estimates put the date around five to ten million years ago, far too late to have experienced Gondwana. And if they did show up early enough to hang out on the supercontinent, it’s strange that no other species of this plant family managed to make it to Africa and India.
The third and final scenario is a little more human. In the 1980s, several biologists came up with the idea that
R. baccifera might have crossed the ocean with the help of sailors, potentially 16th century merchants taking on the East India Route. Before they left from Brazil, this theory goes, they gathered up one of the rainforest’s most beguiling plants,
R. baccifera, which dangled gracefully from the trees and, thanks to its ability to survive without soil, could easily survive the journey. Perhaps they used it to brighten up the ship’s quarters, and then left it when they hit port again in Africa.
We may never know exactly how
R. baccifera became an African cactus. But you may choose the most plausible theory for you.