Towards a biogeography of north American charophytes

The great bulk of the world's charophyte literature of the past 100 years o r more suffers from several major limitations. Much is entirely descriptive with but few attempts to ascribe any functionality to the features under c onsideration, or how they adapt such species to their respective ecological niches. Charophyte distributions have been attributed almost entirely to p hysical parameters with virtually no consideration given to the role of aqu atic herbivores or other biotic environmental factors. Furthermore, most wo rkers have focused on relatively restricted areas with little or no referen ce to others either near or far removed. That there is much to be gained fr om a wider focus (both spatially and conceptually) that incorporates greate r conjecture as well as enhanced collaboration is here suggested. How are t he charophyte floras of one region similar to, or different from, those of another, and, of particular significance, 'Why?' The authors, being North A merican, focus on that continent bur with the firm conviction that most gen eralities applicable there hold equally true for other landmasses, and have done so for the previous 10, if not 100, million years. This account focus es first, if somewhat superficially, on 14 widely distinct North American c harophyte communities (plus South American Lake Titicaca) and then in great er detail on four of those. Among other issues considered are how species r ichness relates to latitude; why some geographical entities support more ch arophyte species than do others; the extent to which charophyte floras refl ect the availability of different habitats; the contributions of herbivory to the preceding; the stability of the North American charophyte flora; the ecological considerations most often reflected by charophyte zonation and how-or to what extent-range extensions reflect niche preferences or require ments. While the authors well appreciate just how minimal their efforts may appear a century hence, at least they hope to have placed on the table som e considerations with which colleagues from other landmasses may agree, dis agree or suggest modifications.