gametophyte reduction

[David Hershey]

Foster and Gifford's text, Comparative Morphology of Vascular Plants,
mentions that there are a few fern species which exist almost entrely as
gametophytes with the sporophytes rare and small (Science 142: 1483-84).
Perhaps they are an illustration of how the sporophyte could possibly
have become reduced and dependent on the gametophyte. 

David Hershey
dh321 at excite.com


Dana Ann Dudle wrote:
> 
> Hi All--
> 
> After such helpful and interesting responses to my question regarding
> polyploidy, I have decided to try yet another question on y'all:
> 
> What were the intermediate steps between the dominant, photosynthetic
> gametophyte and reduced sporophyte present in the non-vascular plants
> (bryophytes), and the dominant sporophyte that is present in all vascular
> plants (as far as I have been able to discern).  The oldest fossils of
> vascular plants that are most often referenced in textbooks and review
> articles, e.g. Cooksonia and Rhynia, are called sporophytes...
> 
> IT seems as if this was a very important development in the evolution of
> plants, and yet I have found very little reference as to HOW this change
> occurred.  Does anyone know of fossil evidence or living transitional
> forms that may give some insight into this major change in the focus of
> the alternation- of- generations in land plants?
> 
> I have always been taught that "mosses have dominant gametophytes, and
> ferns have dominant sporophytes", but I have not questioned the "how or
> why" until I started writing lectures and preparing classes on this topic.
> 
> Any hints or leads would be greatly appreciated (as well as speculations!)
> 
> Thanks,
> Dana
> *********************************
> Dana A. Dudle
> Dept. of Biological Sciences
> DePauw University
> Greencastle, IN  46135
> ddudle at depauw.edu
> *********************************