March 2017 Plant Profile: Corokia cotoneaster

Corokia cotoneaster may not be the first plant that you notice in the landscape, but it might be the plant keeps your attention the longest. This plant’s divaricate branching (having branches of wide angles) and its tiny dark evergreen leaves give it a sparse and angular look which is not a common sight among the green gardens in the Pacific Northwest. Add a spring bloom of tiny fragrant yellow flowers followed by red berries in autumn and this plant can be a focal point of any garden. Its common name is wire netting bush which describes the plant’s unique form.

James Galther
Corokia cotoneaster at UC Botanical Garden, Berkeley

As a slow growing shrub it attains a height of 3 meters (8 ft) and width of 2 meters (7 ft), but would take a very long time to do that in the PNW. Found in rocky scrubby areas in its native range in New Zealand, this plant is tolerant of very dry conditions and takes full or filtered sun. The ideal spot in the PNW garden is a warm sunny location with well drained soils. An established plant can withstand a freeze to about 20 degrees (Zone 8) but young plants might need some protection from winter exposure. It takes shearing well and can be used as a hedge. But why deny it of its wonderful natural zig zag form?

James Galther
Corokia cotoneaster flower, at UC Botanical Garden, Berkeley

The genus Corokia is found in New Zealand (ten species) as well as a few species on islands close by. The name is derived from the indigenous Māori name for Corokia: korokio. These plants, in the Argophyllaceae family are all woody. Of all the Corokia species found in New Zealand, Corokia cotoneaster has the widest distribution, occurring from sub-alpine scrub to coastal cliffs. As a result, the form of this plant is quite varied throughout its range. Hybrids (mostly with C. buddleioides) and cultivars exists in the horticultural world. ‘Little Prince” is a cultivar of C. cotoneaster which is smaller in size and has more grey, downy hairs on new growth. This species makes an excellent container plant if properly drained and can also be used for bonsai.

Frank Vincentz
Corokia cotoneaster

The unique zig-zag form of Corokia cotoneaster is found in many shrub species across New Zealand.  This branching pattern is referred to as divaricate and often describes a plant with wide angle branching and little or no leaves growing on the terminal ends of these branches, the outer canopy. The New Zealand section of the Pacific Connections Garden at the Washington Park Arboretum has several species of these evergreen divaricate shrubs. One popular idea regarding why these uniquely structured shrubs are more common in New Zealand than anywhere else on the globe has to do with the now extinct flightless bird, the Moa. These birds were thought to have co-evolved with shrubs like Corokia cotoneaster, and the plant’s form was a response to their browsing pressure. However, research shows that the abundance of divericate shrubs may likely be a mechanism to avoid photoinhibition while photosynthesising under certain winter conditions (Howell et al 2002). This branching architecture provides protection for the leaves of these evergreen plants under bright sun during cold winter days.

Daniel Sorensen
Corokia cotoneaster in the snow. New Zealand Forest, Washington Park Arboretum.

There are several standout specimens of Corokia cotoneaster located in the McVay Courtyard at the Center for Urban Horticulture and many more plants are establishing in the New Zealand section of the Pacific Connections Garden at the Washington Park Arboretum. This plant gets better with age and can be admired throughout the year. It should be in bloom from April to May so be sure to take notice on your next visit.

Common name:  Korokio or Wire Netting Bush
Family: Argophyllaceae
Location: Several plants are on display in the McVay Courtyard at the Center for Urban Horticulture. Numerous specimens can be found throughout the New Zealand Forest’s Mountain and Snow Tussock zones at the Washington Park Arboretum (Grid 7-3E. 8-3E and 9-3E), and in the New Zealand Entry Garden (6-3E and 6-4E)
Origin: New Zealand
Height and spread: 6-8 ft in height and 4-6 feet in width. Cultivar ‘Little Prince’ is smaller, attaining a height of about 4 ft.
Hardiness: Cold hardy to USDA Zone 8

 

Frank Vincentz
Corokia cotoneaster leaf

 

 

Cited:

Howell C. J., D. Kelly Turnbull and M. H. Turnbull.  2002. Moa Ghosts Exorcised? New Zealand’s Divaricate Shrubs Avoid Photoinhibition. Functional Ecology, Vol. 16 (2), pp. 232-240.