You can see them growing on the roadside in places like Bermuda--thousands of miles away from the land where the species originated. One gelled leaf we cut and brought home with us had enough soothing ointment to last an entire vacation season of sunburns.
Easing the pain of sunburn is just one of aloe's many uses. One of the most widely used natural products in the western hemisphere, aloe is worth an estimated $13 billion a year, according to Stephanie Pain, writing in New Scientist.
And while humans have been exploiting its healing powers for centuries, only now are scientists beginning to unravel the course that this interesting plant has taken since it 'left' its native habitat back in Africa.
Actually, Africa is not entirely accurate, as Pain writes that the particular species of aloe that has become one of the world's favorite natural products likely traces to one of the plant's earliest offshoots, in the Arabian peninsula.
Olwen Grace of London’s Royal Botanic Gardens at Kew and her colleague Nina Rønsted, a specialist in the evolution of medicinal plants at the Natural History Museum of Denmark in Copenhagen, have enlisted the help of botanists in Africa and Europe to gather and examine the DNA of nearly 200 aloes from their widest geographical range.
"By comparing key DNA sequences," writes Pain, "the team built a near complete picture of how the hundreds of aloes living today are related, how they evolved and when and where they originated."
They trace the first aloes to southern Africa, around 19 million years ago. According to Grace et al, they began to diversify as the subtropical climate started to become more seasonally hot and dry. From here they spread north to the Horn of Africa.
Around 5 million years ago, they believe, a few dispersed north to the Arabian peninsula, some west across central Africa, and some east to Madagascar. The result: a rich variety of new habitats.
Among those that appeared on the Arabian peninsula is a group of seven species that share many features with Aloe vera. Sure enough, a comparison of their DNA showed that these are its closest relatives (BMC Evolutionary Biology, vol 15, p 29). “So we now know that Aloe vera originated somewhere on the Arabian peninsula,” says Grace. “That gives us a starting point in the search for the beginnings of the Aloe vera phenomenon.”
The Arabian peninsula is where the real migration launched, Pain writes. And it was probably by accident. The main item moving northward from this hub of trade in ancient times was incense --but Grace et al believe the traders brought aloes with them for their own medicinal purposes.
And they caught on. In a big way.
“People in the region had probably been using and cultivating it for generations, and traders would have carried it as a sort of living medicine chest,” [Grace] says. It helped that the plant is easy to transport. Cut leaves stay fresh and useful for a long time, and plantlets produced by suckering survive a long time without soil or water – even seemingly dead ones will grow if you plant them. “This is the most likely way it spread to Egypt, Ancient Greece and Rome, then to India and later to the Americas,” says Grace.
The history of the plant's migration is not the only target of their studies, as Rønsted makes clear. In spite of its popularity, scientists still lack the clinical evidence that aloe's soothing gel has the healing powers claimed for it.
To this end, they are focusing on the plant's polysaccharides, as they have yet to fully understand the chemistry of these complex sugars in the plant.
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