"We had been on the biosecurity website to check it ... that's why we're so horrified with the mistake."
She said the store picked up a small amount of the hornwort from a person who had also mistaken it for oxygen weed, or elodea canadensis.
Bay of Plenty Regional Council biosecurity officer Andrew Blayney said a large number of aquatic plants were easily confused.
"It's not hard to make the mistake. I wouldn't expect the general person to be able to ID them."
The National Pest Plant Accord listed the unwanted plants that could not be sold, propagated or distributed in New Zealand, he said.
Mr Blayney encouraged people to be aware of the accord, especially when dealing with any aquatic plants.
It was an eye-opening experience for the Papamoa store and one that shocked the small family business, Mrs Thorne said.
"We've always tried to be ethical and provide our animals with the best conditions."
She was happy to speak out to warn others against the easy mistake.
"If in doubt, always check with the experts," she said.
Mr Blayney agreed.
"If people are ever unsure the regional council can help them with the ID."
Hornwort
The regional council has previously described hornwort as one of the most damaging aquatic weeds.
*It is widely established in the North Island and is found in fresh water.
*Hornwort was originally propagated as an aquarium and ornamental pond plant, but it is now banned from sale or distribution under the Biosecurity Act.
Pest plants
*All unwanted plants are listed on the National Pest Plant Accord.
*Bay of Plenty Regional Council biosecurity officers can identify plants for people who are unsure: 0800 884 880.
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