Coriaria angustissima

Coriaria angustissima, commonly known as small-leaved tutu, is a low-growing bushy shrub endemic to New Zealand's South Island.

Small-leaved tutu is a native bushy shrub known for its narrow thread-like leaves. It has many erect branches that are feathery with dark green, thin pointed leaflets that are often 7–10 mm long and 1–2 mm wide and have soft branches with a square cross section. Black fruit is arranged in a brief spike.^[1] The cross-section of the branches is square. The tiny, bell-shaped flowers hang down. The petals are about the same size as the green sepals and there are ten achenes in the black fruits.^[2]

The species is endemic to New Zealand and is found mainly in the wet highland in the south of New Zealand, particularly along the west side of the Southern Alps and on Stewart Island.

Coriaria angustissima is a subshrub that grows in subalpine and subarctic biomes at varying altitudes of 300 m up to 1500 m.^[3] Small-leaved tutu thrives in well-drained soils and open woodlands, where its roots can spread extensively.^[4]

It typically takes around one year for small-leaved tutu to reach full maturity. Seeds of C. angustissima often germinate after rainfall, usually in spring or early summer. The seeds have a hard coat and may require a period of dormancy due to colder months affecting metabolic activity before germinating.^[5] Once seeds germinate, they enter a seedling stage where they grow roots and shoots. During this phase, the plant is particularly vulnerable to drought but adapts to the harsh desert environment. C. angustissima then enters a phase of vegetative growth, where leafy branches develop as well as a woody tangled structure solid enough to withstand windy conditions. When flowering occurs, male and female flowers are formed on separate plants (dioecious).^[5] After pollination, female plants produce small, fleshy, dark purple to black berries that are somewhat toxic to humans but serve as food for various bird species. These berries often ripen around November – February, where seeds can then be dispersed via consumption by birds. Coriaria angustissima can reproduce sexually through seed sprouting, where new shoots will emerge from the root system, enabling the plant to spread in areas where conditions are favourable.

Deer are renowned for eating the leaves of small-leaved tutu, as well as rabbits. However, almost all parts of the Coriaria species are poisonous, including the pollen. For that reason, livestock as well as predator species to the plant often avoid grazing even though they may be attracted to damaged or wilted leaves.^[6]

Tutu concoctions may have been used in Māori medicine. Insanity was treated using mixtures of several herbs, which were also used as laxatives and more frequently, as bandages for wounds and fractures. Some Māori recreational beverages were made using juice from tutu fruit.^[6]