The sweet potato Ipomoea costata, an exception to the lack of tubers and farm-associated plants in Australia
(writing in progress)
The plants eaten by Aboriginal people in Australia were all wild, as opposed to selectively bred.
This is because the indigenous people practised no domestication. In other words, there was no farming of plants in aboriginal Australia.
With this in mind, it is unsurprising that most of the genera of plants eaten as staples by Australian aboriginals belong to genera (e.g. Acacia, Marsilea, Terminalia, Santalum) that are not cultivated elsewhere on Earth for the same plant-part eaten in Australia.
A partial exception is Solanum. This is a genus common and diverse in Australia. Its fleshy fruits were eaten, providing a link with e.g. eggplant, cultivated on other continents.
Dioscorea is another partial exception, because this genus has been domesticated on other continents as a cultivated yam.
But the most striking exception to this pattern is Ipomoea, the genus to which the sweet potato belongs.
The cultivated sweet potato (Ipomoea batatas, https://www.inaturalist.org/taxa/62941-Ipomoea-batatas) is a member of the Convolvulaceae, originating in central America.
It is now the major staple in the highlands of New Guinea, as well as on certain islands in the Pacific (as far south as New Zealand), and in parts of the Philippines.
The cosmopolitan genus Ipomoea (https://en.wikipedia.org/wiki/Ipomoea) contains about 500 species, of which some are indigenous to Australia.
In particular, Ipomoea costata (https://www.inaturalist.org/taxa/1347903-Ipomoea-costata) grows naturally in semi-arid tropical Australia, in biomes vaguely comparable with the Kalahari of southern Africa. Its tuber was a favourite food of aboriginal people.
What strikes me about I. costata is how similar it is to the cultivated species I. batatas, including the size of the tuber (please see photos below).
Ipomoea batatas has been bred into hundreds of cultivars. However, it remains essentially similar to this wild species in the remotest parts of Australia.
I happen to know Ipomoea well, because I have long grown it in my garden in Perth, Western Australia.
The surprise for me:
The plant growing in my garden has been domesticated for thousands of years, being selectively bred by the indigenous Americans, and then further selectively bred by various groups of people, after being taken abroad by the Spanish.
So one would expect it to be much-altered from its ancestor. And yet the plant the Australian aboriginals dug out in the wild in the Tanami Desert was, to all intents and purposes, similar.
So, in a strange way the sweet potato I grow in my garden is a form of 'wild food’, and probably one of the more ‘natural’ of cultivated crops.
I often eat the tubers raw, which is perfectly wholesome. This lacks the sweetness of the cooked tuber, but instead has a refreshing, bland crispness. In this practice, am I eating the closest thing to starchy 'wild food' that one can grow in plenty in an inner-city garden, without commercial fertilisers?
My interpretation assumes that the tuber of wild I. costata is free from toxins, much like cultivated I. batatas. That assumption needs checking.
Another noteworthy point:
Whereas the Kalahari has diverse tubers, similar biomes in Australia have few. Ipomoea costata is a remarkable exception, because it is not only a tuber, but a large one, quite as large as anything I expect to grow in my garden.
My current view:
What is remarkable is that the indigenous people in central America and Australia both ate ‘sweet potato’, despite the cultivation of this plant by the former people and the gathering only of wild plants by the latter people.
There was a categorical difference in culture between these peoples. The indigenous Americans were farmers, while the indigenous Australians were not. Nonetheless, in this case, they both ate essentially the same food: large tubers of Ipomoea.
In North America, an indigenous sweet potato is Ipomeoa lacunosa (https://www.inaturalist.org/taxa/135262-Ipomoea-lacunosa), illustrated below.
However, the interesting thing is that this species is toxic with alkaloids, unlike I. costata of Australia. Indeed, I infer that nearly all of the ca 500 spp. of Ipomoea worldwide tend to be toxic.
It is remarkable that, in such a speciose genus, it is really just one species, I. batatas, that is cultivated on any scale.
This suggests to me that the ancestor of I. batatas, in central America, was (much like the true potato Solanum tuberosum, https://www.inaturalist.org/taxa/53858-Solanum-tuberosum) toxic until selectively bred.
What this all seems to add up to is that the tuberous genus Ipomoea tends to be toxic, but the forms found in northern Australia tend for some reason to be non-toxic.
As a result, we had the remarkable situation in pre-European times in Australasia, that:
When Europeans invaded New Guinea, they found the indigenous people using Ipomoea batatas as a staple.
When Europeans invaded northern Australia, across the sea from New Guinea and formerly connected to New Guinea at low sea-levels, they found the aboriginals using Ipomoea costata as a staple in some areas.
The New Guineans were cultivating I. batatas, and presumably breeding it selectively. By contrast, the northern Australian aboriginals were using a completely wild plant that had never been bred selectively. But the remarkable thing is that the food was essentially similar: non-toxic tubers that could presumably be eaten raw.
Come to think of it:
If one goes back farther in time, to say 18 thousand years ago, when Australia and New Guinea were one (a continent called Sahul), there would have been a situation in which the indigenous people would have been eating I. costata, as a wild but palatable plant.
Neither Ipomoea batatas nor any form of farming occurred at that time, because I. batatas was only brought from central America in the Holocene (a few thousand years ago) to New Guinea, long after New Guinea became an island again.
What this adds up to:
We have the remarkable situation that ‘sweet potato’, much as we know it today, was actually eaten by the Australian aboriginals in the Pleistocene BEFORE it was ever produced by the central Americans, and brought via the Pacific to New Guinea.
I think this situation arose because the Australian I. costata was unusual in its environment, lacking indigenous animals that dug up and ate the tubers as would have happened in Africa and also the Americas. Because I. costata was relatively free from consumers, it did not develop toxins.
As a result it did not really need selective breeding. The insularity and nutrient-poverty of Australia effectively ‘domesticated’ the sweet potato for the aborigines.
In summary:
Indigenous Australians eked out an existence on a nutrient-poor, fire-prone continent with few edible plants and no farming. However, a compensating factor was that - because the herbivorous fauna of Australia was so limited - such plants as did occur in Australia sometimes lacked the anti-herbivore defences found on other continents.
So the aborigines found relatively few food-plants, but those that they did find tended to be less toxic than their closest relatives on other continents. If this pattern is valid, I think that the genus Ipomoea may epitomise it.
Ironically, Australian indigenous people were enjoying sweet potato long before anyone else on Earth, and today we find the odd situation that the New Guineans eat a sweet potato which has been through a journey through time and space to get to where it is today, and all it has really done is to emulate the palatability of the original sweet potato of northern Australia.
All the following photos show Ipomoea costata:
http://www.apscience.org.au/projects/APSF_04_3/APSF_04_3_image_01_full.jpg
https://pindanpost.files.wordpress.com/2012/12/imgp0430.jpg
https://pindanpost.files.wordpress.com/2014/04/c4.jpg
https://en.wikipedia.org/wiki/Ipomoea_lacunosa
The following is a source of interesting information on Ipomoea costata, an indigenous sweet potato in Australia: http://www.shaman-australis.com/forum/index.php?showtopic=35011
Points I gleaned:
The plants can grow large, up to 3 m high and with a stem up to 15 cm thick.
The tubers are remarkably deep (I note that even in the cultivated, selectively breed I. batatas there is a tendency for the tubers to be located in hidden spots e.g. under skirting paving stones or where it is hard to dig).
There is a main tuber which tends not to be eaten by the aboriginal people, who eat mainly the tender small tubers.
The small tubers, if not also the large one, seem to be toxin-free and palatable even when raw (much like cultivated sweet potato I. batatas).
The species is common on the coast of the Pilbara in tropical semi-arid Western Australia.
The foliage and flowers, as well as the tubers, are surprisingly similar to those of cultivated sweet potato (I. batatas).
This is my current thinking:
Ipomoea is a cosmopolitan genus of weedy ‘creepers’, which tends to produce starchy tubers.
The plants protect their tubers from animals by a) hiding them as much as possible and b) making them toxic (with alkaloids I think).
Although indigenous people would have encountered Ipomoea on various landmasses, the plant was seldom eaten because of its toxicity. For example, in Africa, as far as I know, Ipomeoa did not feature in native diets.
However, an exception was tropical Australia, where there were so few large animals that Ipomoea enjoyed an island-like existence and, like so many other organisms on islands, lived in a relatively defenceless way.
When the human species colonised Australia about 50 thousand years ago, it found this naturally palatable and wholesome sweet potato in the form of I. costata (which is said actually to be a complex of up to six species).
So, for thousands of years there was a situation in which the human species ate sweet potato more or less only in Australia – as a fully wild plant, not a cultivated one.
Then, much later (about five thousand years ago), the central American aboriginals started to breed the ancestor of Ipomoea batatas selectively to get rid of the ?alkaloids, and the result was the modern, cultivated sweet potato I. batatas.
This farmed species was eventually brought, via the Pacific, to New Guinea, and much later again to New Zealand.
The result was that, at the time when Europeans invaded New Guinea and New Zealand, they found the indigenous peoples eating sweet potato as a staple, much as they found the aboriginals of northern Australia – in some areas – eating sweet potato as a staple.
But little did the Europeans realise that the origins of these sweet potatoes were quite different, and opposite to expectations.
The Australian aboriginals got their sweet potato naturally, without domestication. The indigenous people of New Guinea and New Zealand got their sweet potato unnaturally, after a long process in space and time.
(writing in progress)
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