三叶草属（Trifolium），又名车轴草属。三叶草包含很多不同种类的植物，包括各种颜色的三叶草、以及其他各种植物，是一种广泛分布在欧洲的多年生草本植物。叶子互生，呈长圆形；有特别长的根系，可适应不同的气候和土壤条件，吸收土壤中的矿物质和其他营养，在旱季亦可生存；还可以作为牧草、绿肥作物或者观赏植物，种植车轴草能使土地肥沃。它分布于全世界温带地区。

在西方很多国家（如英国、美国）长有四片叶子的三叶草代表着幸运。因为四片叶子的三叶草被认为是只有在伊甸园中才有的植物。而在有些国家里，扑克牌里面的梅花就是代表幸运的车轴草。

Clover or trefoil are common names for plants of the genus Trifolium (Latin, tres "three" + folium "leaf"), consisting of about 300 species of plants in the leguminous pea family Fabaceae. The genus has a cosmopolitan distribution; the highest diversity is found in the temperate Northern Hemisphere, but many species also occur in South America and Africa, including at high altitudes on mountains in the tropics. They are small annual, biennial, or short-lived perennial herbaceous plants. Clover can be evergreen . The leaves are trifoliate (rarely quatrefoiled, cinquefoil, or septfoil), with stipules adnate to the leaf-stalk, and heads or dense spikes of small red, purple, white, or yellow flowers; the small, few-seeded pods are enclosed in the calyx. Other closely related genera often called clovers include Melilotus (sweet clover) and Medicago (alfalfa or 'cavalry clover').