There are four cultivated species of cotton viz. Gossypium arboreum, G.herbaceum, G.hirsutum and G.barbadense. The first two species are diploid (2n=26) and are native to old world. They are also known as Asiatic cottons because they are grown in Asia. The last two species are tetraploid (2n=52) and are also referred to as New World Cottons. G.hirsutum is also known as American cotton or upland cotton and G.barbadense as Egyptian cotton or Sea Island cotton or Peruvian Cotton or Tanguish Cotton or quality cotton.G.hirsutum is the predominant species which alone contributes about 90% to the global production.
- Gossypium arboretum - Bracts are more or less triangular and closely invest bud and flower. Bracts have 4-5 teeth at the apex. Bolls are tapering and profusely pitted with prominent oil glands. Bolls open widely on maturity. This species is also known as Indian cotton.
- Gossypium herbaceum - Bracts flare widely from the bud, flower and boll. They have 6-8 teeth. Bolls are round and rarely with prominent shoulders. Bolls are smooth or with few shallow pits and few oil glands. Bolls open slightly when ripe.
- Gossypium hirsutum - Flowers do not have red spot at the base of petal. The staminal column is short. The anthers are loosely arranged on the staminal column. Anther filaments are larger in the upper region than in the lower region. The capsule surface is usually smooth.
- Gossypium barbadense - Bracts are very large which cover the flower bud completely. The staminal column is long on which anthers are compactly arranged. The anther filament is of same length. Bolls are large and deeply pitted with black oil glands. Red spot is present at the base of petal. Bracts are united at the base in diploid cottons and free in tetraploid cottons. Diploid cottons have high degree of resistance to biotic and abiotic stresses, whereas tetraploid cottons have high yielding capacity and good fibre quality.