Native button daisies, Leptinella (once known as Cotula), include a number of species under threat nationally. One of the smallest and most threatened is L. dispersa subspecies rupestris, which grows only between Castlecliff to Hawera, and in one site near the Waikato River mouth.
That means 90 per cent or more of all known plants are in our region. But what makes it 'threatened'? Firstly, each plant is either male or female and there is no known place where male and female now grow together.
That means no seed. Secondly, the plants form creeping mats on wet sand ledges on mudstone sea cliffs that are falling away into the sea. Sea level rises will accelerate loss of habitat for this button daisy and other coastal plants.
It has already gone from places where it grew a decade ago, like the Kai-iwi stream mouth where sea cliffs collapsed.
In a few places with relatively stable sea cliffs, like those between Castlecliff and Mowhanau, exotic plants (weeds) are out-competing it. Cultivating this button daisy has been met with mixed success. And all this adds up to another native species on the brink of extinction.
Every three years the New Zealand Indigenous Vascular Plant Panel meets to review the threat status of all native plant species.
The panel met a few weeks ago and, for each plant, assessed its degree of threat in the wild based on how many plants in each site; the number of places they are found; their productivity (the production of flowers, fruit and young plants); and the types of threat such as browsing animals, land development, disease and illegal harvesting.
Each species is then assessed as being either under threat or not. Those calculated to be under threat are classified, in descending order of threat, as threatened (nationally critical, endangered, vulnerable) and at risk (declining, recovering, relict, naturally uncommon).
The review includes plants that are unnamed but which are believed to be distinct and which are likely to be named someday. That often means when funds are available to pay for the research needed to name a new plant.
Our local sea cliff button daisy was regarded as "naturally uncommon" three years ago but, from recent surveys by local botanists, new awareness of its decline should lead to a higher threat status in the 2012 revision.
Plants for which not enough is known to decide on a threat status are consigned to "data deficient"; people are invited to collect data on these for re-assessment in three years' time.
The results of the 2012 re-evaluation of threat status are awaited eagerly by everyone involved in plant conservation. They help decide which species need most field effort and research, meaning priorities for time and money. Information, including threat status, and pictures of almost all of New Zealand's named native plants can be seen on the New Zealand Plant Conservation Network's website http://www.nzpcn.org.nz. This website also illustrates more than 50 per cent of New Zealand's weed species.