Horse tail and Horsetail

Horsetail and horse tail are semantically related. In some cases you can use "Horsetail" instead a noun phrase "Horse tail".

Horsetail noun - Perennial rushlike flowerless herbs with jointed hollow stems and narrow toothlike leaves that spread by creeping rhizomes; tend to become weedy; common in northern hemisphere; some in Africa and South America.

Horse tail and horsetail are semantically related. Sometimes you can replace phrase "Horse tail" with "Horsetail", this terms are similar.