AUTOGAMOUS ALLOHOMOPLOIDY IN ALSOPHILA AND NEPHELEA (CYATHEACEAE): A NEW HYPOTHESIS FOR SPECIATION IN HOMOPLOID HOMOSPOROUS FERNS

Morphological and chemosystematic studies demonstrate that three endemic Puerto Rican tree ferns, Alsophila bryophila, A. dryopteroides and Nephelea portoricensis have been hybridizing and have produced a hybrid swarm. Three distinct hybrids are present, one of which is strikingly uniform in its morphology. The population ecology of species and hybrids indicates that the most uniform hybrid is more abundant and has a narrower ecological adaptation than its parents. The hybrids are fertile diploids and are producing F₂ segregates which resemble species from other islands in the Greater Antilles. An hypothesis for the stabilization of hybrid reproduction at the homoploid level, autogamous allohomoploidy, is proposed. The hypothesis explains the sharing of unique characters between sympatric species pairs of Alsophila and Nephelea in the Greater Antilles and in Central and South America. It is suggested that other genera of homosporous ferns have also speciated by autogamous allohomoploidy.