I’ve also been experimenting with a Hawaiian variety, which has white flesh streaked with pink and is even pithier than the Papua New Guinean varieties.  It has smaller grape vine shaped leaves that make a tasty salad green and works in vegetable stir fries really well.

My aunt in Indiana in the USA grows this variety too. Given that Indiana gets extremely cold and snowy in winter I’m amazed it grows there. As everyone in Papua New Guinea knows kaukau doesn’t like frost.

My impression was that sweet potato was a staple confined to the warmer southern states; it is the state vegetable of North Carolina for instance.

The Yanks also like to candy their kaukau using sugar. Yuk!

Kaukau originally came from South America. It was being grown in Peru 5,000 years ago.

There is some contention about how the sweet potato got to Papua New Guinea. It was originally assumed it was brought there by Portuguese sailors about 400 years ago but it is also known from archaeological sites in Hawaii and New Zealand around 700 AD.  Incidentally, Portugal is one of the few places in Europe where kaukau is grown.

It is now thought that kaukau was brought to the Pacific by Polynesian seafarers who had sailed to South America and back. The variety found in the archaeological sites is not generally grown much now and the kumara of New Zealand is more like the orange stuff in Australia.

I doubt that whoever originally brought kaukau to Papua New Guinea realised the impact it would have – it caused a major social and culturally revolution.

Nomadic hunters and gatherers became sedentary agriculturists, which in itself required major changes in the way a society organises itself. There was also a population explosion, not only humans but also pigs, which were domesticated and fed kaukau.

The changes that this humble plant brought to PNG mirrors the changes that came to the western world 10,000 years ago when humans started to cultivate cereals in what was then the lush landscape of the Middle East.

What is now called the Melanesian Way evolved into its recent historical form only after the widespread introduction of kaukau. Kaukau enabled the development of the bigman system and its offshoot the wantok system.

Papua New Guinea, as it is today, is essentially a product of the humble sweet potato.

A lot of the stuff in my garden comes from seeds and cuttings purloined from all sorts of places. My kaukau originally came from a farmers’ market.

I grow pawpaws from the seeds originally from market-bought fruit and all my pineapple tops and pups go into the ground. I pinched my banana tubers from the local botanic gardens.

My orange-coloured, thick skinned lemon trees come from ancient wild plants I found on Fraser Island. I’ve even grown tomatoes from seeds taken out of tins imported from Italy.

One thing I have noticed is the difficulty of germinating seeds taken from the hybrid varieties I’ve bought at garden centres.

The production from these plants tends to diminish with each new seed planting until I eventually end up with sterile plants. This year I grew a tomato whose fruit resolutely refused to ripen.

This is, in effect, a ploy by the people who genetically modify the plants to force you to keep buying their seeds or seedlings.

Normally when you grow something and replant its seeds it adapts to your soil and climate, a sort of natural modification. That way you end up with more and more productive plants. Not so with genetically modified hybrids apparently.

A well-known giant agro-chemical company has produced hybrid sweet potato resistant to many diseases and sells it in places like Africa and now some people report the diminishing returns they get year after year.

In the USA the company aggressively pursues and prosecutes farmers who use seeds from their hybrids, most notably corn. The company insists that the farmers are stealing.

Hybrid kaukau is available in PNG and some people are using it. I’ve seen it in the Markham Valley and it is indeed a bigger, healthier and more productive plant.

I’m not sure how the replanting of cuttings, tubers and seeds is going but the agro-chemical company story is worth bearing in mind.

Back in the 1960s there used to be a takeaway at the back of a Chinese store in Mount Hagen that made fish and chips out of kaukau and tin fish when it couldn’t get ordinary potatoes and frozen fish.

Since then I’ve always relished sweet potato chips. Just don’t try it with the orange stuff, it tastes dreadful.

In fact, I might just go and dig up a few kaukau for tea tonight.