Cotton (Gossypium hirsutum L.) is one of the most important cash crops in the world, and potassium (K) is an important limiting factor for cotton farming. Therefore, it is critical to improve K-use efficiency by selecting or breeding cotton genotypes with high K-use efficiency. Through a pot experiment with low-K soil, this article documentes the differences in vessel element anatomy and root hair traits between two cotton genotypes with different K-use efficiencies at both seedling and boll stages. Experimental results showed that at the seedling stage both frequency and length of root hair in the genotype with high K-use efficiency were significantly greater than those of the genotype with low K-use efficiency, but the frequency and diameter of vessels were not significantly different between the two genotypes. In the boll stage, the vessel frequencies in root, stem, petiole, and carpophore; root hair frequency, and length of high K-use-efficiency genotype were all significantly greater than those of the low K-use-efficiency genotype. The denser and longer root hairs were often found and accompanied by thicker vessel elements in the genotype with high K-use efficiency. This means the genotype had greater nutrient uptake and transportation capacity. The root hairs, vessel elements in root, stem, petiole, and carpophore, formed a complete system for nutrient uptake and

translocation. The results from this study provide valuable information for the breeding of high K-use-efficiency cotton.