Ferns are closer cousins of roses than of clubmosses
Ferns, horsetails and clubmosses were long lumped together as spore plants, or pteridophytes. Genetics broke the group apart: ferns and horsetails turn out to be more closely related to seed plants than to the clubmosses they were filed with. The old name survives in everyday use, but not as a true branch of the tree.
A pteridophyte is a vascular plant, with water- and food-conducting tissues, that reproduces by spores instead of flowers or seeds. That hidden way of reproducing earned such plants the old label cryptogams. Their life cycle alternates between two separate, free-living generations, a small gametophyte and the larger spore-producing plant with true roots, stems and leaves.
Ferns dominate, making up nearly 90 percent of living pteridophyte diversity. A 2014 consensus by Maarten Christenhusz and Mark Chase counted about 10,535 fern species against roughly 1,300 lycopods, the clubmosses, spikemosses and quillworts. For scale, lycophytes account for under 1 percent of living vascular plants, while seed plants number around 260,000 species. Among the features that mark out ferns in molecular studies are sperm cells that may carry anywhere from 30 to 1,000 flagella.
Naming has been messy. In 1997 Paul Kenrick and Peter Crane introduced monilophytes, from a word meaning bead-shaped, as a scientific stand-in for ferns including horsetails. Christenhusz and Chase later criticised the term as irrational, noting an older name was already available. Lycopod, by contrast, means wolf-plant. The catch-all fern allies, covering spore plants that are not ferns such as horsetails, whisk ferns and water ferns, is also discouraged because it is not a natural grouping.
The Pteridophyte Phylogeny Group's 2016 system now recognises two related classes: lycophytes, with three living orders, and ferns, with eleven. Horsetails survive as a single genus, Equisetum, and the largest fern order, the Polypodiales, contains 26 families. Botanists who study them still call themselves pteridologists.
Source: Pteridophyte
