"And so it went on and some serious doubt crept into my mind, I must have this wrong, this is a very rare plant only known in very low numbers in widely scattered populations, I've made a mistake.
"But what Tom and I were looking at were the largest Olearia gardneri trees ever seen along with everything from young seedling plants and everything in between, an amazing find that had somehow gone unnoticed till then."
A comprehensive management plan has since been developed to enhance the current population, introduce plants to other tiny populations in Wairarapa, and set up new populations in other suitable covenanted sites.
Local Forest & Bird members are also helping out, clearing weeds from the site and collecting seeds and cuttings which have been passed on to Norfolk Road Native Nursery to grow for the plant's recovery programme.
Already 200 plants are ready for planting out in autumn.
Until this discovery, the total number of known plants in the wild was estimated at 160, but Mr Thompson counted 374 of them at the Wainuioru site.
A previous attempt by Masterton schools in 2010 to regenerate the plant in a programme unrelated to the National Trust on a different property in Wainuioru was unsuccessful.