Coprosma robusta

Karamu is a large bushy shrub that grows up to 6 meters (20 feet) tall.[1] Branches are stout with no hair.[2] Domatia (small holes on the back of the leaf at the intersection of veins) and stipules are significant characteristic features of Coprosmas.[3] Karamu stipules are black, hairless and obtuse with slightly serrated margin that are united at the base [2]

The glossy leaves of karamu range from 5 to 12 centimeters (2.0 to 4.7 inches) long, with elliptic-oblong shape and acute or obtuse leaf apex and with obvious veins.[4] Leaves are dark green on the blade and light green on the back,[2] are thick, and the midrib is not raised on the upper surface.[1]

Flowers are small and white, axillary, dense, have four lobes and have a different appearance in male and females. Male flowers are dense, glomerules with a campanulate shaped corolla and have four stamens; female flowers are compound with a tubular shaped corolla. Stigmas are obvious.[4] The best flowering period is between August and September.[2]

Karamu in fruit

Fruit are often dark orange-red to red, oblong to narrow ovate drups.[4] The best fruiting period is between April and May.[2]

Karamu is endemic to New Zealand.[4] However, it is gradually becoming naturalized in areas of the south-east coast of Australia such as Victoria and Tasmania and has been rated as a weed threat there.[5][6]

It is widely distributed across New Zealand in both the North and South Islands. On the Chatham Islands between Waitangi and Owenga, there is a small area where karamu has become naturalized.[2] They can often be observed naturally in lowland forest. Judging from the distribution map on New Zealand Plant Observation,[2] the distribution of karamu increases with the differentiation in lower altitude which means more karamu in the North Island.

In Canterbury, karamu is found on Banks Peninsula in fragments of regenerating native bush and bush remnants. Additionally it is also found in forest margins and edges of the montane and lowland forests in the southern alps at the start of the Canterbury planes. Karamu can also be found in the urban environment of many Christchurch city green spaces (e.g. park like Riccarton Bush).[7]

Karamu can be widely found near coastal, lowland and lower montane areas. It can also grow within shrub lands and expansive areas within dense trees such as lowland forest.[2] However, the population decreases in lowland forest such as beech and kahikatea forests.[4] Normally karamu is a hardy plant that can adapt to infertile soils, poorly drained and exposed lands. It can also grow in a large range of altitude varying from 0 to 1,200 meters (0 to 3,937 feet) under full sun to shady, windy and frosty circumstances.

Karamu is an extremely hardy plant that can grow in a large range of environmental conditions from full sun to shady, from dry to moist, and can tolerate frost and wind. The mature fruit can endure a minimum temperature to −8 °C (18 °F) and the leaves can endure a minimum temperature −7 °C (19 °F) before they get irretrievably damaged.[11] It grows best in a moist soil[5] which is not too acid, although they have the ability to live in poor soils.[12] They can also be found in coastal conditions, lowland scrub, swamps and rock associations.[13]

Herbivorous mammals such as goats (Capra hircus) and deer (Cervus elaphus) have a severe impact on karamu, and hares (Lepus timidus) and rabbits (Oryctolagus cuniculus) eat the seedlings.(Brockie, 1992). Additional consumers of karamu are Batracomorphus, Batracomorphus adventitiosus, leafhoppers and Membracoidea.[14]

Birds which disperse karamu seeds include native bellbirds (Anthornis melanura) and Tuis (Prosthemadera novaeseelandiae), indigenous silvereyes (Zosterops lateralis), and introduced blackbirds (Turdus merula), and song thrushes (Turdus philomelos).[15] Seeds can be dispersed a long way and into areas of more mature forest.[7] According to the database in Encyclopedia of Life,[2] additional species that interact karau are Acalitus, Acalitus cottieri, Eriophyid mites, European greenfinch, and goldfinches.

Karamu and mycorrhizal fungi can make a symbiotic mutualism in roots system. Because mycorrhizal fungi can supply water and nutrients to the plant. Experiments with karamu shows its growth is assisted by the presence of mychorrhizal fungi assuming there is sufficient phosphorus in the soil.[16]

Karamu will sometimes act as a host plant to support other plants including podocarp, totara and yellow-wood family.[2]

Juvenile shoots can be applied to release inflammation or bladder problems if boiled and then the liquid drunk. The leaves are believed by Maori to have the ability to deal with kidney troubles and bark can be and used to treat stomachache and vomiting.[17]

The mature berries of karamu can be eaten as food, and its leaves used to make a tea drink.[17]

Karamu is rich in dying properties including alizarin and purpurin. Traditionally Maori used it to dye flax (Phormium) fibers yellow.[4] Sometimes leaves of karamu were put on stones and dye the food and preserve them after a hangi.[17]

Baptists used the leaves in a ceremony and green karamu branches will be held by tohunga in tohi for newly born babies.[17]

Karamu is noted for its quick bushy growth and for this reason is commonly cultivated and frequently used for revegetation projects.[7]