Blackcurrant can damage both unopened and open flowers when the temperature falls below . The flowers at the base of the strig are more protected by the foliage and are less likely to be damaged. In midsummer the strigs of green fruit ripen to edible berries, very dark purple in colour, almost black, with glossy skins and persistent calyxes at the apex, each containing many seeds. An established bush can produce about 4.5 kilograms (10 pounds) of fruit each year. Plants from Northern Asia are sometimes distinguished as a separate variety, "Ribes nigrum" var. "sibiricum", of which "Ribes cyathiforme" is considered
Empetrum nigrum Empetrum nigrum Empetrum nigrum, crowberry, black crowberry, or, in western Alaska, blackberry, is a flowering plant species in the heather family Ericaceae with a near circumboreal distribution in the northern hemisphere. It is also native in the Falkland Islands. It is usually dioecious, but there is a bisexual tetraploid subspecies, Empetrum nigrum" ssp. "hermaphroditum, that occurs in more northerly locations and at higher altitude. Evolutionary biologists have explained the striking geographic distribution of crowberries as a result of long-distance migratory birds dispersing seeds from one pole to the other. The metabolism and photosynthetic parameters of "Empetrum" can be altered in