PHYLETIC LINES IN THE MODERN FERNS1 JOHN T. MICKEL2 Before we can begin to discuss the overall phyletic lines of the ferns, we must ask ourselves the rather old and trite but nevertheless crucial question, "What is a fern?" From what we know of the fossil record there were no true ferns in the Devonian, but there was a great array of now extinct groups of so-called ferns in the Carboniferous. How do we circumscribe the group, and is there any reason to question the naturalness of this taxon? Traditionally we define it as any megaphyllous plant reproducing by spores. From the great diversity of plants that we have seen placed in "the ferns" in the fossil record it seems quite possible that some groups could well have arisen separately from Devonian or Carboniferous ancestors before we would have called them true ferns. I am not proposing that we answer the question at this moment, nor am I certain that we can answer it at this point in time, but I want to keep the question open as we address ourselves to the overall view of the evolutionary lines as seen in the modern ferns. Another major difficulty that must be mentioned before we can begin is that morphologically we are still in somewhat of a mess regarding the characters of the ferns. In an attempt to prepare an objective way of producing a phylogeny with the aid of computerization, the systematic characters of the ferns were examined rather closely. A broad comparison is extremely difficult or impossible at this time. What are the characters? We actually know little about any of them. In the first place in many cases we cannot make comparisons between the taxa. We may have information on certain characters for certain taxa, but it generally is difficult to compare the information we have between major groups of ferns. Secondly, we do not know what we are looking for in all characters. For example, in most descriptions of ferns their vestiture is described as consisting of hairs or scales and only rarely with any sort of qualifiers, such as clathrate scales or acicular hairs. In some cases the same type of scale or hair is described as being present in totally different and unrelated groups of ferns, yet no detailed study has been made to see whether in fact the two are really the same. We have virtually no information on another aspect of vestiture, namely theparaphyses. What types are there? What is their importance to the plant?What is their phylogenetic significance? There are many other characters injust this saine state of non-recognition. The work of Bower along these lineswas extremely important, but the work is far from finished. We are still in thecrosier stage of morphological and phylogenetic study in the ferns. The study of phyletic lines in ferns has taken into consideration in the pastvirtually exclusively the modern ferns and ignored the fossil ferns. The reasonsfor this are good ones. The ferns of the Paleozoic are extremely diverse and 'Supported in part by a grant from the National Science Foniidation (GB-30859X). 'The New York Botanical Garden, Bronx, New York 10458.Axx. MissouRI BTr. GARn. 61: 474-482. 1974.