GENUS COMMUNITIES AS A SYSTEMATIC TOOL IN THE STUDY OF NEW WORLD BOTRYCHIUM (OPHIOGLOSSACEAE)

Summary Problems in the taxonomy of Botrychium (Ophioglossaceae) are outlined and discussed. Species interpretation has been controversial because many taxa are little known, poorly collected, highly variable, and subtly differentiated. A method of study based upon the tendency of the species to coexist with each other in the same habitats is discussed, and examples from our field work are given. The "Genus Community Method" and the related "Mutual Associates Method" allow critical comparisons to be made. Cohabitation of two or more species without successful interbreeding demonstrates biological discreteness and confirms that the character differences are most likely genetically fixed. A summary of our knowledge of what pairs of species have been found to co-exist is given for subg. Sceptridium and subg. Botrychium. For the former, the major associations occur in eastern North America and tropical America north of Panama, including the Antilles. For the latter, the major associations occur in western North America. As many as seven species may grow together in one habitat. We conclude that the genus may not be as difficult taxonomically as previously believed. By discovering and analyzing genus communities of Botrychium, we can show which taxa are consistently and persistently distinct. If species in plant genera are subtly different, traditional ways of testing whether their differences are genetically controlled are by techniques such as reciprocal transplants or common garden experiments. However, growing Botrychium plants is very difficult, presumably because of their delicately attuned mycorrhizal relationships. In addition, the growth rate of these plants is so slow that ordinarily only a single leaf is produced per year. (Primordia for several years are contained within the bud, and only one primordium matures each season.) We have had, therefore, to find a substitute for experimental cultivation, and we have adopted a method of comparison based upon the tendency of closelyrelated botrychiums to grow in the same habitats. In spite of popularity with morphologists and floristicians, the taxonomy of these plants remains in an extremely unsettled state. The identifications of many North American herbarium collections border on the chaotic, and the classifications presented in many manuals are at variance with the natural populations. We have recently intensified our field investigations of these plants, and during 1980 and 1981 we examined over 4000 plants in more than sixty localities from Canada to Central America and the Antilles. Many botrychiums are rare and inconspicuous. The rarest is the Pumice Moonwort, B. pumicola, known from only two populations in southern Oregon; from our recent observations we estimate that there are no more than 1500 living individuals. Botrychium mormo of the Upper Great Lakes area (Wagner and Wagner, 1981) was collected only twice prior to 1950, and these specimens were confused with other, more common species. There were apparently no collections of B. montanum of the Northwest prior to 1976, but we found it to be common locally in many localities in Montana, where it had unquestionably been overlooked. The bizarre B. paradoxum, which has no sterile segment but two fertile segments, was not discovered until 1969, at which time it was thought to be an aberrant specimen of some other species.