This article was published in The Fringe, February 2015
There are two species of Corokia growing in the Waitakere Ranges, predominantly along the coastal margins although scattered widely throughout.
The smaller leaved form is Corokia cotoneaster and is a tightly divaricating shrub up to 2m. It is a curious looking plant with a wide range of forms from the almost leafless, grey twiggy look, to a lush green mass of tiny leaves 2cm round. Twice a year the shrub transforms itself, firstly into a golden haze of yellow starry flowers in the spring, then in autumn it is covered in berries. This is a great example of the classic New Zealand divaricating shrub showing off the form shaped by millennia of moa browsing. The outermost, newer twigs have virtually no leaves for a browsing bird to eat. To get a meal the frustrated moa would try to wrench a twig off the plant but the 'divaricating' branch network simply stretches till the bird lets go. The essence of a divaricating branch is that each node changes direction at about 45° from the line of growth, creating a zig-zag pattern. Conversely, the Corokia is happy for the Moa and other birds to have a meal of its berries and these are displayed prominently in shades of yellow, orange and red.
C. cotoneaster grows on dry rocky headlands as well as in coastal scrub, thriving in the dry exposed conditions. Indeed there is a particular form growing at North Cape that has so adapted to the extreme exposure that it has evolved to be no more than a 50cm high shrub spreading to 1m after many years.
The other Corokia is Corokia buddleioides which prefers slightly more sheltered, shady conditions. It is quite distinctive with 15cm long leaves which are a bright glossy green on the upper surface, and a fuzzy white underneath. The flowers and fruit are less numerous but quite similar in size and shape to those of the C. cotoneaster. This Corokia does not have a divaricating form and can grow to 3m tall in the shade.
There is a third Corokia, Corokia macrocarpa, which grows naturally on the Chatham Islands and it is the largest, up to 6m tall, with mid-sized 8cm leaves. It is equally tough in exposed conditions and makes a great hedge responding well to tight clipping.
For those who need more than a selection of three species there are innumerable hybrids between them which provide a great array of forms, colours and textures. Some are naturally occurring hybrids which occur when the two parents grow in close proximity. Others have been developed by plant breeders, a strange breed of nurserymen, who think they can improve on nature.