Kowhai = yellow in te reo Maori. It is our unofficial national flower (I don’t think we have an official one), and a tree we see throughout NZ. There are 8 recognised species of Kowhai found in NZ. The 2 types of Kowhai tree we commonly see for sale in nurseries are Sophora tetraphylla – endemic only to the north island, and Sophora microphylla which is endemic to both islands. They flower late August – October just when we need a splash of sunshine colour at the end of winter, and they attract birds looking for nectar eg Tuis & Kereru (wood pigeon).
Sophora microphylla is smaller with leaves 6 mm long and flowers 3 cm long. They grow up to 6m tall.
Sophora tetraptera’s  leaves are 1–2 cm long and flowers  3 cm-5 cm long, and grows taller up to 8m.
Another Kowhai becoming more popular in gardens is a prostrate version. A spreading cultivar sold in nurseries is Sophora ‘dragons gold’. I have planted this successfully on a few jobs around Auckland – it grows quickly to approximately 2m tall x 4m wide – a great filler on big sites.
The only pest problem I have encountered in Auckland, is our native Kowhai moth. This moth can strip all the leaves from any type of Kowhai. Usually the leaves will grow back, but occasionally the tree will not revive and die. The caterpillars are very difficult to see, but I have successfully hand removed lots of them off a small tree. Derris dust is difficult to apply to a big tree, but here is a link with other control suggestions http://www.rnzih.org.nz/Plant_Doctor/WG196_Caterpillars_on_kowhai.htm