Also known as pingao, the plant, which was considered to be in gradual decline in 2004, topped more than 100 species in the poll.
Network president Philippa Crisp said pikao was becoming increasingly important because of its role in stabilising sand dunes and creating a beach contour that was not so vulnerable to storm events and sea level rises.
"Pingao may be our only sustainable hope for coastal protection."
It was also important because the yellow-green to orange leaves, when dried, were used by Maori for weaving.
Parts of the plant were also said to have medicinal properties.
Department of Conservation botanist Mike Torsen said pikao had disappeared from Dunedin, except for areas planted by the Dunedin City Council or coastal care groups.
It could still be seen in some areas on Otago Peninsula and the Catlins.
"It's a really useful plant, as it holds the sand dunes together."
It could be grown in gardens although it preferred deep, sandy soil, he said.
Dunedin City Council parks and reserves team leader Martin Thomson said it had been displaced in many areas by marram grass.
Efforts had been made to reintroduce the plant, which along with its ability to trap sand, was an attractive-looking plant and hardy, he said.
"It's one of the few things that survives the environment, the sea spray and salt."
It had been planted along the coastal margin in front of the Brighton Surf Club and in amenity plots at the Esplanade in St Clair and along John Wilson Ocean Dr.
Also on the top 10 were three species on the verge of extinction, including the fish guts plant, which historically was found in Otago and Canterbury and made its home in sparsely vegetated ground, such as dried out river beds.
In the past few decades it had been found only in the Upper Waitaki Valley and Lake Lyndon, in inland Canterbury.
The other two plants were Bartletts rata (Far North) and kakabeak (East Coast).
The top 10 also included pohutukawa, two species of rata and the tree nettle.
