That, George Hazelman pointed out, "is the Duva plant. You can use it to poison fish and they're safe to eat."
This useful tip came during a walk through the Wainadoi Spice Gardens, about 25km outside Suva, in a section devoted to traditional Fijian medicinal plants. "It's illegal to use duva now. But it does work"
How, I wondered, did he know this. George, an obvious enthusiast for his work at the gardens, grinned - he had tried duva once just to see if really was effective.
"You grind up the root and put it in a bag. When you get to your fishing place you squeeze the bag and a milky fluid comes out. The fish only need one sniff of that stuff and they're gone."
And had he also checked that the dead fish were safe to eat. "Oh, yes, it was fine. No problems. I ate them and I didn't get sick."
The spice gardens are being developed as a tourist attraction, as a place where people can come and see all sorts of exotic fruits, herbs and spices, as well as the indigenous plants of Fiji. But the main role of the gardens is to provide raw material for Spices of Fiji, which produces the likes of vanilla beans and essences, nutmeg and black pepper.
The operation was set up a few years ago by 82-year-old Dr Ronald Gatty, Australian born and Fiji raised, who has returned home after making a fortune in the United States and is trying to help locals raise their living standards.
"The idea is to try out different commercial crops to see what can be grown successfully in Fiji in the hope that others will copy us," said George.
"The sugar industry here is dead - they just don't know it yet - because our growers with their 10-acre farms can't compete with the factory farms in Queensland or Chinese labour at $1 a day.
"What we need are crops that can be grown economically on small farms that farmers can switch to."
And have they found any? "Oh, yes, several," said George."Our main crop is vanilla. But nutmeg and black pepper are going well too."
Wander round the spice gardens and you discover that there's a lot more plants than those being tried.
"Try this," he said, crushing a few leaves from an attractive dark green tree. I identified a strong smell of cinnamon. "That's it. Cinnamon."
The actual cinnamon spice, though, comes from the bark. "We reckon this would be ideal for Lau" - a group of islands in eastern Fiji - "because they're very short of firewood. If they plant cinnamon they could harvest the bark and then have the rest of the tree to play with."
In short order he also pointed out cardamom and cloves, betel and oil palms, avocado and noni, botebote koro - "good for healing wounds" - and vutu raka which is another fish poison.
Perhaps the most intriguing of the spices is nutmeg, an apricot-coloured fruit which splits open when ripe to reveal two nuts, the red mace and the black nutmeg.
"It's all useful," said George happily. "We've just found that in Grenada they use the flesh to make jams or pickles. And the mace and the nutmeg are spices,"
Best of all the company's nutmeg is selling well. "We can't meet the demand here in Fiji," said George. "We haven't had to think about exporting it ... which we do with our vanilla because the people here would rather use the artificial essence." The look on his usually smiling face showed what he thought of that.
By now we had wandered round the gardens and heard countless stories about the plants but I was still keen to hear about the two piles of roots I had noticed on the way in. They were, it turned out, two varieties of ginger.
"The big one is normal ginger and the small one is Jamaican ginger which is supposed to be much hotter."
With a grin George broke off a piece and handed it to me asking, "What do you think?"
Actually I like ginger, especially when it's crystallised, and the hotter the better, so I took a big bite ... and almost gasped. It was very hot stuff.
Unfortunately it seems there isn't any crystallised Fijian Jamaican ginger on the market yet but when there is I'll be a customer.
Getting there: Air Pacific flies from New Zealand to both Nadi and Suva. See airpacific.com
Where to stay: Tambua Sands is a charming garden resort on the Coral Coast. See tambuasandsfiji.com.
What to do: Wainadoi Spice Gardens, are on the web at spicesfiji.com.
Further information: See Tourism Fiji's website.