PUSHING THE BORDERS

The Pseudopanax laetus was one of the first shrubs I planted when we moved here six years ago. Up until a couple of weeks ago it looked magnificent, now many of the leaf petioles are going brown causing the whole leaf cluster to drop. There is no visible sign of above ground pest so I suspect a problem down in the soil.
Reading online I found a piece on the 'Royal New Zealand Institue of Horticulture' website that says " One thing that many New Zealand natives really hate is to have "wet feet". Poor drainage and wet, humid conditions encourage root rots, which unfortunately are usually fatal."
My top soil is very free draining but beneath that there is heavy shillet soil that holds more water. My guess is that the wet winter and subsequent wet spring and summer have done for it. I won't know for sure until I stop crying and dig it out, gutted :(

We have had several unexplained losses of established trees and shrubs in the last year, I have been too lazy to send bits off to see whether its Fireblight, Phytophthora, or maybe even Honey fungus, its very disappointing :(

Sorry to hear of the problems with the P. laetus
I agree with Charlies ideas on sudden death, assuming it was not a cultural or positional problem as you fear it might have been.
My P. chatamica always flowers well on our chalk near Brighton, and has self seeded.
They are small, but could send one which could be grown on in a pot until large enough to plant out?