There are three varieties of knotty kale: common kale, purple kale, and wrinkled leaf kale (Figures 10-2 through 10-7).

(A) Common Kale

It has a smooth leaf surface without significant wrinkles, slightly prominent leaf midribs, and green to dark green leaf color. It is one of the most widely cultivated and largest varieties in China and around the world.

(2) Purple kale

Leaf surface and ordinary kale, smooth and no significant wrinkles, but its outer leaves and ball leaves are purple-red. It turns blackish-purple when fried, and is generally preferred to be eaten cold and raw. The cultivated area is far less than that of common kale, and it is often cultivated as a special dish in some areas of China, with the area expanding year by year.

(C) wrinkled leaf kale

The leaf color is like ordinary kale, green to dark green, but the leaf is very developed because of the leaf flesh between the veins, forming an uneven leaf surface folds. The ball leaves have a soft texture and good flavor, and can be fried. It is also often cultivated as a special dish in some parts of China, but the cultivated area is not large. It is more widely cultivated in Europe.

Can be divided into three types: oblate spherical, round spherical, and pointed spherical (Figures 10-4 to 10-7).

(A) oblate spherical

Leaf ball flat round, larger, most of the late maturing varieties. Stronger winter, as spring kale planting is not easy to occur uncooked shoots, some of the varieties of winter is very strong. Disease resistance, heat resistance, cold resistance is strong. Completion of the stage of development is not sensitive to the length of light requirements. Picked seed plants flowering early, flowering period of 30 ~ 40d, plant height is generally between the round sphere and pointed sphere. China's spring and summer cultivation of medium and late-maturing kale and fall and winter kale are mostly of this type. It is widely cultivated in Japan.

Figure 10-2 Wrinkled-leaf kale

Figure 10-3 Purple kale

Figure 10-4 Ordinary kale (rounded)

Figure 10-5 Ordinary kale (oblate)

Figure 10-6 Ordinary kale (pointed-globe-1)

Figure 10-7 Ordinary kale (pointed-globe-2)

(ii) Globe-shaped

Leaf globes are globular or nearly round, mostly early or medium-maturing varieties. Leaf ball tight, ball leaves crisp, good quality. However, some varieties in this type of winter is weak, as spring kale planting, such as sowing too early or improper cultivation management is prone to immature shoots. Disease resistance, heat resistance, cold resistance are poor. Completion of the stage of development must have a long time of light. Pick the seed plants flowering late, flowering period of 40 ~ 50d, flower shoots height of 150cm or more. In the north of China for early spring kale cultivation are mostly such varieties. At present, in the United States, Britain, the Netherlands, France, Denmark, India and other countries cultivated for these varieties.

(C) pointed ball type

Also known as the bull's-eye shape, the top of the leaf ball is pointed, mostly early-maturing varieties. Stronger winter, as a spring kale planting is not easy to uncooked shoots, disease resistance, heat resistance is poor, but cold tolerance is strong. Completion stage development is not sensitive to the length of light. Picked strains of flowering early, flowering shoots height of about 120cm, flowering period of about 30d. These varieties are generally used for early spring cultivation in all parts of north and south China, especially in the Yangtze River Basin, widely used as overwintering cultivation. In Britain, the Netherlands, France, Russia and other countries also have more cultivation.

Three, according to the cultivation season and maturity classification

Generally can be divided into spring kale, summer kale, autumn and winter kale and a year of large late-maturing kale four types. Some types can also be divided into early, medium and late maturity according to the maturity of early and late.

(A) spring kale

Suitable for winter sowing seedlings, spring cultivation type. Generally good quality, but resistance to disease, heat resistance is poor. According to its maturity can be divided into early maturing spring kale and medium and late maturing spring kale. Early-maturing spring kale can be harvested 40-60d after planting, and the leaf ball is mostly rounded or pointed spherical. Medium and late-maturing varieties of spring kale harvested 70 to 90d after planting, the leaf ball is mostly oblate.

(ii) summer kale

Generally refers to the type of varieties that are sown in April to May, harvested and marketed in August to September in the two-season crop area. Generally more heat-resistant, and better disease resistance. Leaf color is darker, more wax powder on the leaf surface, mostly flat round medium maturity varieties; but in recent years, suitable for high altitude or high latitude cold areas, summer planting of early maturity round ball type varieties of cultivation area, there is a trend of increasing year by year.

(C) fall and winter kale

Suitable for sowing in July to August, fall and winter harvest marketed types of varieties. Generally more resistant to disease, and better heat tolerance. According to the maturity of early and late can also be divided into early, medium and late maturity three categories. Early maturing varieties are mostly nearly spherical, planted about 60d harvest; late maturing varieties are generally oblate spherical, planted 70 ~ 90d harvest.

(D) a year of large late-maturing type

This type is mainly distributed in China north of the Great Wall and the Qinghai-Tibetan Plateau and other alpine areas. Because of these areas of short frost-free period, no obvious summer, and this type of varieties of fertility and longer, and therefore more than one year a mature. General March to April sowing, harvested in October, they are one of the main winter storage vegetables in these areas.

Four, according to the botanical characteristics and ripeness of comprehensive traits classification

Tomson (Tomson, 1949) according to the botanical traits and ripeness of the two traits of the integrated performance of the nodular kale is divided into eight types, that is, the Wakefield, spreading the wings of the group, Copenhagen group, the Netherlands, the flat head, the bulging head of the group, wrinkled-leafed kale group, Danish bulbous head of the group, group A, the Volga group, the Red Kale group, and so on. Each type has its similarities in botanical traits and ripeness (Table 10-1).

Table 10-1 Knotting kale by botanical traits and ripeness of the comprehensive trait classification

V. By seedling vernalization type classification

Knotting kale for green body vernalization type plants, that is, the requirement to grow into a certain size of the plant to feel the low temperature and through the stage of development. However, the length of the nutrient growth period required to complete stage development, the size of the plant, and the length of time it takes to feel the low temperature and light vary according to the type of variety. Pihara (1959) classified by seedling vernalization type, that is, according to the characteristics of the conditions required to complete the stage of development, the nodular kale is divided into spring sowing late type, autumn sowing type, summer sowing type, northern spring sowing type, tropical type and other five ecological types.