Kōwhai

Kōwhai tree in full bloom, before foliage has emerged

The eight species of kōwhai are:[3]

• Sophora chathamica, coastal kōwhai
• Sophora fulvida, Waitakere kōwhai
• Sophora godleyi, Godley's kōwhai
• Sophora longicarinata, limestone kōwhai
• Sophora microphylla, small-leaved kōwhai
• Sophora molloyi, Cook Strait kōwhai
• Sophora prostrata, prostrate kōwhai
• Sophora tetraptera, large-leaved kōwhai[8][9]

Sophora tetraptera foliage

Sophora tetraptera flowers, foliage and seed pods

Most species of kōwhai grow to around 8 m high and have fairly smooth bark with small leaves. S. microphylla has smaller leaves (0.5–0.7 cm long by 0.3–0.4 cm wide) and flowers (2.5–3.5 cm long) than S. tetraptera, which has leaves of 1–2 cm long and flowers that are 3–5 cm long.

The very distinctive seed pods that appear after flowering are almost segmented, and each contains six or more smooth, hard seeds. Most species have yellow seeds, but Sophora prostrata has black ones. The seeds of Sophora microphylla can be very numerous and the presence of many hundreds of these distinctively yellow seeds on the ground quickly identifies the presence of a nearby kōwhai tree. Many species of kōwhai are semi-deciduous and lose most of their leaves immediately after flowering in October or November, but quickly produce new leaves. Flowering of kōwhai is staggered from July through to November, meaning each tree will get attention from birds such as tūī, kererū and bellbird.[10] Tūī are very attracted to kōwhai and will fly long distances to get a sip of its nectar.

The wood of kōwhai is dense and strong and has been used in the past for tools and machinery.[1]

Sophora is one of the four genera of native legumes in New Zealand; the other three are Carmichaelia, Clianthus, and Montigena.[9]

Studies of accumulated dried vegetation in the pre-human mid-late Holocene period suggests a low Sophora microphylla forest ecosystem in Central Otago that was used and perhaps maintained by giant moa birds, for both nesting material and food. The forests and moa no longer existed when European settlers came to the area in the 1850s.[11]

Kōwhai can be grown from seed or tip cuttings in spring and autumn.[12] The dark or bright yellow seeds germinate best after chitting and being soaked in water for several hours. They can also benefit from a several minute submersion in boiling water to soften the hard shell and then being kept in the same water, taken off boil, for several hours to soak up the water.[13] Young kōwhai are quite frost tender, so cuttings or seedlings should be planted in their second year when they are 30 cm or higher.[14]

If grown from seed, kōwhai can take many years to flower, the number of years varies depending on the species.[15]

S. prostrata, sometimes called "little baby", is used as a bonsai tree. It grows up to two metres high, has divaricating[16] stems, and sparse smallish leaves.[17]

All parts of the kōwhai, particularly the seeds, are poisonous to humans.[18] However, there do not appear to have been any confirmed cases in humans of severe poisoning following ingestion of kōwhai in New Zealand.[19]

Traditionally the Māori used the flexible branches as a construction material in their houses and to snare birds. The kōwhai flowers were a source of yellow dye. Also, when the kōwhai flowers bloom, in late winter and early spring, it is time to plant kumara (sweet potato).[20]

Māori also used the kōwhai tree as medicine. Wedges made of kowhai stem were used to split wood, it was used for fences and in whare (Maori hut) construction, implements and weapons.[21] The bark was heated in a calabash with hot stones, and made into a poultice to treat wounds or rubbed on a sore back[22] or made into an infusion to treat bruising or muscular pains.[23] If someone was bitten by a seal, an infusion (wai kōwhai) was prepared from kōwhai and applied to the wounds and the patient was said to recover within days.[22]