North Island large-leafed kōwhai is the tallest of eight species of sophora endemic to New Zealand, although the genus is found throughout Asia, America, Europe and the Pacific. It belongs to the pea family, which includes gorse, broom and the native kākābeak. Growing to 12 metres, Sophora tetraptera is suitable for a street or garden tree if carefully staked when young, and is great for attracting tui, bellbirds and kākā. Two features make the kōwhai unusual among our native plants: first it is semi-deciduous, and secondly, unlike most New Zealand plants whose blooms are white and inconspicuous, its flowers are a striking sunny yellow. (In te reo Māori the word for yellow is kōwhai) The springtime blooms on the barren branches of the kōwhai are a sign for Māori to plant kūmara and gather kina.
The tree was also used for medicinal purposes: bark collected from the sunny side of the trunk was steeped in water to make wai kōwhai, which was used to treat pain, wounds, skin diseases, and constipation. It is said that in 1925 when the ‘Invincibles’ All Black, George Nepia sustained a severe leg injury and was threatened with surgery to avoid blood-poisoning, he instead chose the kōwhai cure. Two weeks after bathing in wai kōwhai he captained Hawkes Bay to victory over Taranaki. All parts of the tree contain a toxic alkaloid called cytisine, or sophorine, which seems to help people stop smoking, but is also a powerful purgative. After a group of whalers stole the grog of an old Bluff brewer he got revenge next time they were in port by putting boiled kōwhai leaves in his brew. "For 12 hours straight they were erupting at both ends." (Vennell, The Meaning of Trees)
This particular tree is on the Meadow Walk.
