Fern ally and Horsetail

Fern ally noun - Pteridophytes of other classes than Filicopsida.

Horsetail and fern ally are semantically related. In some cases you can replace term "Horsetail" with "Fern ally", this terms are similar.

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.

Fern ally and horsetail are semantically related. You can use "Fern ally" instead a noun "Horsetail".