Sphenophytina

Sphenophytina

"The horsetails. Homosporous vascular plants with jointed stems marked by conspicuous nodes and elevated siliceous ribs and sporangia borne in a strobilus at the apex of the stem. Leaves are scalelike. Sperm are motile. ALthough now thought to have evolved from a megaphyll, the leaves of the horsetails are structurally indistinguishable from microphylls. There is one genus, Equisetum, with about two dozen living species."

References

Biology of Plants, Fourth Edition, Worth Publishers Inc., Stanford University, Peter H. Raven and Helena Curtis, ©1971