INCHOATE SPECIATION IN CERATOPTERIS: AN ANALYSIS OF THE SYNTHESIZED HYBRID C. RICHARDII X C. PTERIDOIDES.

Abstract

Interspecific hybridization in the homosporous ferns usually results in the formation of sterile diploid or triploid hybrids. Sterility in these instances is the result of extreme differences in chromosome homologies between the parental taxa and the subsequent lack of normal chromosome pairing in the hybrids. Hickok and Klekowski (1973) have demonstrated that this type of hybridization is accompanied usually by the meiotic production of unreduced spores by the sterile hybrid; these spores have the potential to produce polyploid derivatives of the hybrid (allopolyploids) that have the ability to reproduce through normal sexual processes. Through this process, reticulate evolution of the type documented by Manton and Walker (1953) and Walker (1955, 1961) inDryopteris and by Wagner (1954) in Asplenium can be seen to be a major feature in the evolution of homosporous ferns. A notable exception to this production of sterile hybrids and fertile polyploid offspring in the ferns was documented by Walker (1958) in Pteris where hybridization between P. quadriaurita and P. multiaurita resulted in the formation of completely fertile F1 diploid hybrids that exhibited complete bivalent formation at meiotic prophase. The subsequent production of F2 segregates and backcross hybrids to parental types resulted in the production of a hybrid swarm in which all of the taxonomic