木贼属是蕨类植物的一属，共有15个物种。此属植物几乎分布在全世界上，除了澳洲和南极洲之外。它们是多年生草本植物，有会在冬天死去的（大部份的温带物种）或为常绿植物的（某些热带物种和温带物种「木贼、蔺木贼、斑纹木贼」和「节节草」）。大多有0.2至1.5公尺高，但沼生问荆可达2.5公尺高，且热带美洲物种的巨木贼可达5公尺高，墨西哥木贼则可达8公尺高。

在此类植物中，叶子大幅地退化于轮生体中，部份则和节鞘相结合。茎部是绿色的且可行光合作用，并有中空、有节与有脊线等特征。在每一节点上可能有或没有分枝的轮生体；但若出现了的话，其分枝除了较小外，和主干没有差别。

Equisetum (/ˌɛkwᵻˈsiːtəm/; horsetail, snake grass, puzzlegrass) is the only living genus in Equisetaceae, a family of vascular plants that reproduce by spores rather than seeds.

Equisetum is a "living fossil" as it is the only living genus of the entire class Equisetopsida, which for over one hundred million years was much more diverse and dominated the understory of late Paleozoic forests. Some Equisetopsida were large trees reaching to 30 meters tall. The genus Calamites of the family Calamitaceae, for example, is abundant in coal deposits from the Carboniferous period.