The genus of Sophora, or Kowhai as we Kiwis know it, comprises around fifty species of trees and shrubs found in the tropics and the more temperate parts of North and South America, Asia, Australia and here in New Zealand.
Regarded by most New Zealanders as our national flower, Kowhai are among the most beautiful of our flowering trees and may indeed be included among the most beautiful trees in the world.
Previously just three species of Kowhai were recognised in New Zealand, but in a groundbreaking study in 2001, scientists from Landcare Research and the Department of Conservation (DoC) named five new species. All eight species have different growth habits, leaves, flowers and flowering times, as well as different habitats.
One or other of these species can be found in most parts of New Zealand, from the coast to mountain areas, in forest, on open hillsides or along rivers.
Three species of Kowhai are found in Northland. Sophora fulvida is more common in the Waitakere Ranges around Auckland. In Northland this species occurs at Maunganui Bluff, Bream Head and near Mt. Manaia on volcanic rock outcrops. It is a small to moderate tree, up to 10 metres high with one main trunk. The leaves with tiny leaflets are crowded and often overlapping.
Sophora chathamica occurs throughout the North and South Islands. It is considered relatively uncommon in parts of the North Island. It most commonly grows on alluvial river terraces, flood plains and lake margins in mixed podocarp/hardwood forests.
The most common Northland Kowhai is Sophora chathamica. It occurs in mainly coastal and lowland sites in Northland, like the Tutukaka coast, also around Auckland and on most northern offshore islands through to Wellington and the Chatham Islands. The Wellington and Chatham Island occurrence of this Kowhai is not considered natural but the result of deliberate Maori plantings. A confederation of Waikato and Taranaki tribes invaded Wellington and then the Chatham Islands. These tribes have traditions of deliberately planting Kowhai for spiritual and medicinal purposes.
The most common northland kowhai is Sophora chathamicaGuy Bowden
Other species of Kowhai are Sophora godleyi, which grows on sandstone and mudstone areas in Rangitaiki to eastern Taranaki, and Sophora molloyi, more of a shrub than a tree with a very long flowering time. It grows on harsh and inhospitable sites on dry exposed headlands around Cook Strait, Kapiti Islands and parts of the lower North Island. One of the finest selected forms is from Stevens Islands in the Cook Strait and is known as the cultivar 'Dragon's Gold'.
Sophora tetraptera is a small spreading tree up to 10 metres found originally growing along stream-sides and lowland forest margins from East Cape to Hawkes Bay.
Sophora longicarnata is a very distinct plant with slender habit, very small leaflets and pale yellow flowers. This Kowhai grows on limestone rocks in the Takaka district northwest of Nelson.
Sophora prostrata is a densely divaricating, bushy shrub up to 2 metres, found in grasslands and rocky places in the eastern lowland mountain regions from Marlborough to South Canterbury. Two of these plants are growing in Laurie Hall Car Park above the waterfall.
Medicinal use of Kowhai has long been known to the Maori and also many other cultures throughout the world where the genus of Sophora grows.
An infusion of the bark was drunk for internal pains, applied externally for bathing bruises and for removing internal blood clots. In 1925 famous Maori All Black fullback George Nepia burst a blood vessel in his leg while playing. A doctor advised operating, but Nepia opted for a Kowhai cure, lying in a bath of boiled Kowhai bark for two hours with a series of small nicks in his leg. It drew the infected blood out of his leg and in a week Nepia was back playing.
Kowhai prefer to grow in full sun and need good drainage. The flowers hold great appeal to native birds. Tui and wood pigeon enjoy the nectar. The Kowhai moth can cause considerable damage but in healthy trees the defoliation is only temporary.