This is probably the plant I got the spores from (15 month old Blechnum) There was also a B. nz. Nearby so I’m sure it’s one or the other. The young plants are very vigorous with long and searching roots. Any suggestions much appreciated.
Blechnum parent plant
The plant in your pictures is not Blechnum nova-zealandiae. It looks to me like Blechnum wattsii. You can have a look at my plants here (and page forward one)
See here for a way of distinguishing these plants