Environment Canterbury's Waimakariri zone biodiversity officer Jason Butt made an unexpected find during a recent visit to Silverstream Reserve, near Kaiapoi, a rare Gratiola sexdentata.
''I know a few botanists have been looking out for this since one was found at the Groynes (near Christchurch) 15 years ago,'' Mr Butt said.
''It's about happening to be in the right place at the right time.''
A Gratiola sexdentata was once found at the Groynes, or Otukaikino, on the south side of the Waimakariri River 15 years ago, but ''has not been seen since''.
''At the time it was known as the only population east of the Main Divide,'' Mr Butt said.
''As the Groynes population is no longer extant that makes this population at the Silverstream Reserve the only known population east of the Main Divide, which is significant.''
Mr Butt said he was actually looking for the ''threatened orchid'' at Silverstream Reserve, after finding a plant population at the Groynes a few weeks ago.
''It indicates other species could easily appear. The seeds can wait in the ground for a long time waiting for the right conditions.''
He said the Silverstream Reserve and the Groynes were identical environments, having once been the north and south braids of the Waimakariri River.
''They are both groundwater-fed at least partially from the Waimakariri River and they were very recent braids.
''And they are both low-nutrient sites, with not a lot of soil, which are pretty hard to come by. You tend to hit gravel pretty quickly.''
Mr Butt said the important thing now would be carefully managing the site to ensure the Gratiola sexdentata was not overrun by weeds and trees and to consider whether it could be cultivated at other locations.
Silverstream Reserve Advisory Group chairman Al Blackie said ''everyone in the group is very excited'' about the find.
-By David Hill
