About Ribes nigrum L.
Ribes nigrum L. (blackcurrant) is a medium-sized shrub that grows to 1.5 by 1.5 metres (5 by 5 feet). Its leaves are alternate and simple, measuring 3 to 5 centimetres (1+1⁄4 to 2 inches) in both breadth and length, with five palmate lobes and a serrated margin. All parts of the plant have a strong aromatic scent. The plant produces flowers in racemes called "strigs" that are up to 8 cm (3 in) long, holding 10 to 20 flowers. Each individual flower is about 8 millimetres (3⁄8 in) in diameter, with a hairy calyx that has yellow glands; the five lobes of this calyx are longer than the plant's inconspicuous petals. Five stamens surround the stigma and style, and the flower has two fused carpels. Flowers open in succession starting from the base of the strig. Most pollination is done by insects, though some pollen is distributed by wind. The plant is somewhat self-pollinating, but produces more fruit when pollinated by another plant of a different variety. When a pollen grain lands on a stigma, it germinates and grows a slender pollen tube down the style to reach the ovule. This process takes about 48 hours in warm weather, but can take up to a week in cold weather; by that time, the ovule may no longer be receptive. If fewer than approximately 35 ovules are fertilised, the fruit cannot develop properly and will fall prematurely. Frost can damage both unopened and open flowers when temperatures drop below −1.9 °C (28.6 °F); flowers at the base of the strig are more protected by foliage and less likely to be damaged. In midsummer, the green fruit on strigs ripens into edible berries. The berries are very dark purple, almost black, with glossy skin and persistent calyxes at the apex, and each berry contains many seeds. An established blackcurrant bush can produce about 4.5 kilograms (10 pounds) of fruit each year. Plants native to Northern Asia are sometimes classified as a separate variety, Ribes nigrum var. sibiricum, and R. cyathiforme is considered a synonym of this variety. Blackcurrant is native to northern Europe and Asia. Cultivation of blackcurrant in Europe is thought to have begun around the final decades of the 17th century.
