The Origin of the Pteridophyte Flora of Central America

Abstract

The biogeographical relationships among the Central American pteridophytes were first suggsted by Hermann Christ in his introduction to the ferns and fernallies in Primitiae Florae Costaricensis (Bommer & Christ, 1896). Christ distinctly identified among his collections those elements considered by him to be of Mexican origin and those he thought best represented the South American vegetation. In his Geographie der Farne, Christ (1910) published his interpretation of the Central American fern flora, mostly based on the ideas of Carl Werckle (1909), with whom Christ corresponded, and who identified a Mesoamerican vegetational type as quite different from both the true Mexican and the South American counterparts. Winkler (1938) augmented Christ's dicta with the addition of many new records. Recently, Tryon (1972) published on the geographical distribution of the continental pteridophytes and defined Central America as one of his regional (Fig. 1), based on the evaluation of some 400 taxonomic units extracted from floras, monographs and herbaria. In 1975, Lellinger proposed a phytogeographical analysis of the Choco vascular cryptogam flora, which resembles that of the Costa Rican and Panamanian floras. Both Tryon and Lellinger rely heavily on the comparison of lists of species, a method which, in my opinion, can only partly reflect the vegetational history of an area. Rather than repeating their comparative researches and thus reaching similar results, I intend to outline the processes by which Central America has become one of the richest and most complex floristic areas of the world. I begin with the following two premises: a) the Pteridophyta is a very ancient group of plants that probably originated in tropical environments; b) because of geological events, Central America can be divided into an older, northern portion known as Nuclear Central America (Vinson & Brineman, 1963) and a southern, younger territory that comprises the southern parts of Nicaragua, all of Costa Rica, and much of Panama. I believe the first statement will require no further explanation, and the second has had an excellent exposition by Dr. Coney (this symposium, also see Weyl, 1980). Tryon (1972) presented sufficient evidence of the strong affinities between the current Mexican, Central American, and South American floras. I only would like to challenge some of his interpretations, particularly those concerning his definition of centers for speciation and his conclusions regarding long range dispersal in such generalized terms.