Collard greens are various loose-leafed cultivars of Brassica oleracea (Acephala Group), the same species that produce cabbage and broccoli. The plant is grown for its large, dark-colored, edible leaves and as a garden ornamental, mainly in Brazil, Portugal, the Southern United States, many parts of Africa, Montenegro, Bosnia and Herzegovina, southern Croatia,Spain and in Kashmir. They are classified in the same cultivar group as kale and spring greens, to which they are closely similar genetically. The name collard is a shortened form of the word colewort (“cabbage plant”).
The plant is also called couve in Brazil, couve-galega in Portugal, “kovi” or “kobi” in Cape Verde, berza in Spanish-speaking countries, Raštika in Bosnia and Herzegovina and Croatia and Raštan in Montenegro. In Kashmir it is called haak. In Congo, Tanzania and Kenya (East Africa) the plant is called Sukuma wiki.
The Cultivar Group name Acephala (“without a head” in Greek) refers to the fact that this variety ofB. oleracea does not have the usual close-knit core of leaves (“head”) like cabbage. The plant is a biennial where winter frost occurs, perennial in even colder regions. It is also moderately sensitive to salinity. It has an upright stalk, often growing up to two feet tall. The plant is very similar to kale. Popular cultivars of collard greens include Georgia Southern, Morris Heading, Butter Collard (orcouve-manteiga), and couve tronchuda.
The plant is commercially cultivated for its thick, slightly bitter edible leaves. They are available year-round, but are tastier and more nutritious in the cold months, after the first frost. For best texture, the leaves should be picked before they reach their maximum size, at which stage the leaves will be thicker and should be cooked differently from the new leaves. Age will not affect flavor. Flavor and texture also depend on the cultivar; the couve-manteiga and couve tronchuda are especially appreciated in Brazil and Portugal.
Fresh collard leaves can be stored for up to 10 days if refrigerated to just above freezing (1 °C) at high humidity (>95%). In domestic refrigerators, fresh collard leaves can be stored for about three days. Once cooked, they can be frozen and stored for greater lengths of time.
Widely considered to be a healthy food, collards are good sources of vitamin C and soluble fiber and contain multiple nutrients with potent anti-cancer properties, such as diindolylmethane and sulforaphane. Roughly a quarter pound (approx. 100 g) of cooked collards contains 46 calories.
Researchers at the University of California at Berkeley have recently discovered that 3,3′-Diindolylmethane in Brassica vegetables such as collard greens is a potent modulator of the innate immune response system with potent anti-viral, anti-bacterial and anti-cancer activity.