THE SO-CALLED “MEGASPOROPHYLL” OF CYCAS - A MORPHOLOGICAL MISCONCEPTION.ITS BEARING ON THE PHYLOGENY AND THE CLASSIFICATION OF THE CYCADOPHYTA

Abstract

1 The morphological interpretation of the female reproductive organ of Cycas, traditionally a primitive form of a fertile leaf homologue or “megasporophyll”, is reconsidered in the light of typological and phylogenetic evidence. 2 The inquiry into the nature of this so-called “megasporophyll” emphasizes its aberrant structure and in spite of the incongruity in appearance requires its homology with the female “strobilus” of all other Cycadales. 3 The homology of the “megasporophyll” with a cycadalean “strobilus” cannot be accepted without certain restrictions, because it is not subtended by a bract. 4 The paradoxal situation can only be explained by the pseudo-phyllosporous nature of the “megasporophyll” produced by the merging of a “strobilus” and its bract, the resulting structure, by exhibiting a mixture of the characteristics of both the axial ovuliferous organ and the foliar bract, assuming an unusual and typologically incongruous shape reminiscent of a teratological case. 5 The re-assessment of the phylogenetic and taxonomic relationships between the genus Cycas and the other Cycadales indicates that this aberrant form is advanced rather than primitive in respect of its near allies. 6 The alternative interpretation of the reproductive organs of the Cycadales has been discussed in connection with its bearing on the morphology and the phylogeny of other cycadopsid groups, and the existence since early Mesozoic times of an independent hologeny leading to the living cycads is postulated. 7 The diversity of the recent Cycadales most probably reflects an early separation of their ancient lineage into several minor lines of descent.