Primitive pteridophytes, which were the earliest vascular plants, from the Silurian and Devonian. They had slender, tapering, leafless, or scale-bearing stems up to 50 cm high, often with cone-shaped sporangia at the top. Recent classifications also include the living psilophytes in this group. The modern psilophytes (Psilopsida) comprise 4 or 5 plant species of the tropics and subtropics, of which Psilotum (whisk fern) is the best known.
Subjects: Earth Sciences and Geography — Plant Sciences and Forestry.