The bizarre sex life of plants

DW: Where did the idea for your book come from?

John Warren: I've long had an interest in crop plants, and most of my working life has been on the agricultural side of plant ecology, and I was just aware that there were lots of good stories related to these plants that demanded telling.

As soon as I started to think about the thread between these stories, the question became clear: why do we eat such a tiny number of crops? Jared Diamond [an American scientist known for his popular science books] asked that question before, and says we domesticated basically everything we could, and we don't eat many things because they are poisonous. I don't believe that. The reason we don't eat so many of the species out there is because of their sex lives.

What do you mean about their sex lives?

The vast majority of plants have toxins in them. Most flowering plants have complicated biochemistry which at some point evolved to stop some animal or other from trying to eat them - so everything is poisonous. In some case, we breed it out or have enzymes to break it down. But many of them still are really poisonous - yet some of the toxins are actually what attracts us to the plant in the first place. That burning feeling you get from a chili is a sort of toxin, and yet people like hot chilies. Even the majority of plant-based drugs have evolved as grazing deterrents - and yet people can't help taking them, even if it's just caffeine.

But the really key plants for telling the story are orchids. There are 20,000 species of orchids. They really ought to be dead ringers for cultivation, because they have root tubers full of starch and can be eaten. The tubers were the commonest street food in medieval London, and were boiled to make a drink called salep. The reason they are lousy as crops is not because they are toxic or not good to eat. It's that they are the kinky perverts of the plant world.

If you take, for example, the orchids that mimic female bees so male bees will come down and mate with them - you cannot pollinate something like that on a farm scale because there won't be enough male bees.

The exception is vanilla. Vanilla is the only orchid that is a commercial food crop. They are hand-pollinated. It's worth hand-pollinating a vanilla orchid because each vanilla pod is worth about three or four pounds a shot. You can hand-pollinate when you have a really valuable crop - but you can't hand-pollinate a field of wheat or a field of cherries. So you can't have crop plants with really elaborate sex lives.

The 10 most important crops are maize, wheat, rice, potatoes, cassava, soybeans, sweet potatoes, sorghum, yams and plantains. Most of them are wind-pollinated, or are root crops that don't require insect pollination. Plantains don't have seeds, and soybeans can self-pollinate, so aren't dependent on wind.

Are there plants that we did cultivate and eat in the past, but for whatever reason we don't anymore?

There are a whole host of plants that have come in and out of domestication - a lot of the garden fruits like raspberries, blackberries and gooseberries - and other there are plants we eat in times of famine, like nettles. Nettles have been cultivated as an important crop, so there are populations of nettles that don't sting, and are used for making a linen-like material.

Sometimes this is a fashion thing or in the case of a plant like the Alexanders, which were brought over to the UK by the Romans, it grows very early in the year and is a bit like celery. It's just got a stronger flavor. To get you through the winter, when you didn't have freezers or modern transportation, you would have been really pleased to have the first greens of the year.

Now we have the ability to transport greens around the planet, and we can store things in the freezer. So some of the vegetables that used to fill that niche have been dropped because they were a bit strong-flavored or difficult to cultivate, and are no longer thought of as vegetables.

How does this tie in with maintaining food diversity and security?

The book argues that a lot of the things we've cultivated are specifically from highly-fertile maritime environments that are highly dependent on nutrients, so if we are going to be more sustainable in terms of the world's resources, then we should be looking to cultivate plants that are not so hungry in nutrient terms.

Also, we really need to be cultivating more species. If we are going to maximize yields, we should be growing multiple crop mixtures rather than monocultures, which is better not only in terms of the environment, but also for managing pests and diseases.

John Warren is a Professor of Botany at Aberystwyth University, and author of "The Nature of Crops: How we came to eat the plants we do."

The interview has been edited and condensed for clarity.